factory reset

Hey there,

If your iPhone or iPad has iOS 15.2 or later installed, see: How to reset your iPhone, iPad, or iPod touch when you forgot your passcode - Apple Support

If that option is not available, you will need to use a computer. See: If you forgot your iPhone passcode - Apple Support

Have you followed the instructions in the articles I sent you above, these articles will be enough to know how to factory reset your phone since your friend has forgotten his phone code, if you want to add your Apple ID account instead of your friend's account you can do so after resetting it!