Resetting iphone

This is how you restore to factory. Restore your iPhone, iPad, or iPod to factory settings - Apple Support You will only need the Apple ID password if you have the device Activation Locked. If so, and you do not have the password, you will have to recover it, if it is your Apple ID. If it is not your Apple ID and it is Activation Locked, you will need to follow this. How to remove Activation Lock - Apple Support

I believe you'll need to follow this support article

If you forgot the passcode on your iPhone, or your iPhone is disabled - Apple Support

ahh, I just read 'passcode' and thought iPhone passcode, good call