Is it possible to switch to a new phone at home?

Hey I wanted to know if it’s possible to set up your new iPhone at home. Because we’ve been trying to set up my daughters new iPhone 12 mini and I can’t find how to connect her phone to our T-Mobile account on the website. Is there a certain place on the website you can go to or do we have to go into one of the T-Mobile stores? Also she already has a phone (android) we’re just trying to switch her number, cellular data, ect. over to the new one.