Can I unlock a iPhone with the iPhone 12

No. You cannot unlock an iOS device remotely.

And, it is not clear how that device is locked.

Unlock 1 = Apple ID locked (Generic):-> If your Apple ID is locked or disabled - Apple Support

Unlock 2 = Apple ID locked (in AppStore&iTunes):->  If you see a message that says 'Your account has been disabled in the App Store and iTunes'

Unlock 3 = Passcode forgotten:-> If you forgot the passcode on your iPhone, or your iPhone is disabled

Unlock 4 = SIM not supported:-> How to unlock your iPhone for use with a different carrier - Apple Support

Unlock 5 = SIM PIN:->  Contact your carrier asking them for your SIM PUK code

Unlock 6 = Activation Lock:-->  How to remove Activation Lock

Unlock 7 = Frozen device:--> If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support

If you mean something different, please better specify your needs.

Regards

Giulio