I can’t transfer my cellular

If you are experiencing difficulty, then contact your carrier for assistance. They are in charge of your cellular connection.

Assuming that you have a new US-spec 14 and an old nanoSIM …

… a “Quick Transfer” as described here should do it.

About eSIM on iPhone - Apple Support

If your carrier doesn’t support Quick Transfer, simply give them a call and they’ll use an alternative provisioning method.