How do u unlock phone if passcode forgotten?

If your device has iOS 15.2 or later installed, you can reset it without a computer; check out this link→How to reset your iPhone, iPad, or iPod touch when you forgot your passcode - Apple Support. Otherwise you will need a computer:

See this Apple support link→If you forgot the passcode on your iPhone, or your iPhone is disabled - Apple Support

Or watch this companion video ⬇️

After restoring the phone using one of the methods above you can restore your most recent backup.

If you have forgotten your Passcode for your iPhone, you must reset your iPhone. The passcode is not stored anywhere, and cannot be recovered if it is forgotten.

See how to proceed if you have forgotten your passcode here:

If you forgot your iPhone passcode - Apple Support