unlocking A1778 FCC ID:BCG-E3091A IC:579C-E3091A

If you mean the passcode to the phone itself, start here:

If you forgot your iPhone passcode - Apple Support

If you mean that the phone is locked to someone else's Apple ID, there is nothing you can do. That person would need to remove the Apple ID.

See this support article, which applies to that error message: If your computer doesn’t recognise your iPhone, iPad or iPod – Apple Support (UK)