how to unlock xfinity carrier?

You have two (2) options (only one of which viable):

1) Obtain a replacement carrier-unlocked phone - or at least a replacement locked to your desired carrier.

2) Contact Xfinity - who originally locked the phone. Explain to them that you’re not one of their customers but that you’d like them to unlock one of their phones so that you can use it on another carrier.

How to unlock your iPhone for use with a different carrier - Apple Support

Only xfinity can unlock it, if you're eligible.

See also this support article:--> How to unlock your iPhone for use with a different carrier - Apple Support

Regards

Giulio

You need to contact them to see if you can get it unlocked. Start here: How to unlock your iPhone for use with a different carrier - Apple Support