On your new iPhone, go to Settings > Mobile Data > Add Data Plan.
Choose a mobile data plan to transfer from another iPhone. If you don't see a list of numbers, tap Transfer From Another iPhone. This requires both devices to have iOS 16 or later.

Check for instructions on your previous iPhone to confirm the transfer. To confirm, tap Transfer or, if asked for a verification code, enter the code that's displayed on your new iPhone.
Wait for the mobile plan to be activated on your new iPhone. Your previous SIM will be deactivated when the mobile plan on your new iPhone is activated.
If a banner appears on your new iPhone that says Finish Setting Up Your Network Provider's Data Plan, tap it. You will be redirected to your network provider's web page to transfer your eSIM. If you need help, contact your network provider.
Reference - About eSIM on iPhone - Apple Support (IN)
