link to change carrier doesn't work

That's not a link. That's just the name of the carrier for the sim card you are currently using. You cannot change the carrier from there.

If you need to change carriers, go to one of the carriers stores and request a sim card from them, or setup a new plan in Settings->Cellular->Add Cellular Plan

That's not a link...

Is the phone carrier locked? If so, you need to contact your existing carrier and ask if it can be unlocked.

What link to change carrier? What is the final result you are you trying to accomplish?