How do I get my old 4s back to factory settings with an unknown Apple password?

If it's on the latest iOS, then no, as far as i know, there isn't a way. and on top of that, if the password isn't used to unlock it from find my iPhone, then nobody else can ever use that phone. it's yours, and you should never have lent it to a friend without making them use their own apple account on it, or none at all, if they can't remember passwords they set. so without the password, you'd have to take it to apple. they may or may not be able to do anything with it. at best, they will give you some store credit for it, and refurbish it, or take it apart for using as spare parts and / recycle parts they can't use.
they may not give you much, if anything for it now. it's too old. so they may take it and recycle it for you, but you might not get anything out of it.
good luck, and if nothing else, take a lesson from this. don't ever give your phone to somebody else, without unlocking it first, and forcing them to either use their own account, or, if they seem to have trouble remembering passwords they set, then no account.

If you have forgotten your Apple ID password or do not know the Apple ID password and it is on the latest iOS, the only way to get help from Apple is if you have the original receipt. If you don't have that, you will get nothing from Apple. That is the point of activation lock.

Yes there is a way to reset it back to factory settings without you knowing the password you have to hold down the power and home button until you get the Srygley line after it powered back on hold it for a little longer and you get a design, on the phone but you have to have it connected to iTunes for this to work then it'll walk you through three setting process With whatever stranger that you have running on the computer but you need a computer to do it I meant screen reader The only way that I know this is because I have done it myself but when you go to do it make sure you have the phone connected to your computer with iTunes running first before you do the hard reset with the home button and the power button at the same time that's how it will work Then when you get the design we sever or whatever spirit you have running on the computer will analogy that is in recovery mood and I'll walk you through the reset process

anthony is correct. if you put the device in recovery mode, you can then whipe it from itunes. i do not remember if you need the apple id password for this, but i believe you do not. there are many things other there on how to get it into recovery mode so let us know if you have any trouble. it can be a bit tricky.

I was under the impression that even if you wiped the phone clean using DFU mode, it would still require the password of the previously associated Apple ID before it would let anyone use it. The whole point of the activation lock feature is to try to make stolen phones worthless by requiring info that nobody in the stolen phone market knows. Obviously anyone worth his salt who's in the market of recycling, resetting or selling stolen phones knows about recovery mode so that shouldn't work if this feature is worth anything.

Is the Apple ID in question yours or your friend's? It's possible one of you could go through the Forgot Password procedure to try to recover the password. I've never had to do this thank goodness, but it should ask you some security questions which should have been set up earlier.

If none of this works, you're probably out of luck unless you can prove to Apple's satisfaction that you are the original purchaser of the phone.

I understand your situation. Were I in your shoes, what I'd have probably done is, as soon as I got the phone back from my friend, assuming it didn't have any needed data on it, I'd have immediately reset it while my friend still remembered and could tell me the password to the Apple ID in question.

even if you do it through recovery mode, iOS still has to activate. It is tied to a certain apple ID and there is no way to make it forget about that. Its on apple's servers and you need the proof of purchase to prove that it is your phone to have apple even talk to you. Sorry.

There are some truth of each points mentioned here. First, if you have the Find My iPhone set to ON and then never turned this option to OFF. Yes, no matter what you do and even if I do a DFU to the device or even overlay a straight format with a new iOS on it. It will ask for the last AppleID and password that was associated to that device. Now if you had indeed not had the Find My iPhone to that device. All above mention will work just fine and won't need of any kind of AppleID to unlock it. Any AppleID at this point will work just fine.
HTH

Hello,

You can try this to at least identify what apple ID is on the device.

If you don’t already have the find my iphone app, download and install it. Make sure the 4 is on and has either wifi or cellular signal. Launch the find my iphone app and use your apple id and see if the 4 is found. IF not, try your friend’s apple id and see if the 4 comes up. If it’s not found, either find my iphone is not setup on the 4, no apple id is used on the phone or your friend may have lent it out to another friend who used their ID.

IF you can get this part figured out, we can work on the next step.

HTH and good luck.