How can I get the AT&T Startup Screen (boot)?

[Android Central Question]

After loosing my AT&T Galaxy S6 I replaced it with a New (3 year old) unlocked Sprint Galaxy S6. I had AT&T setup it up and it generally works but I still have the Sprint start up screen. How can I change it to the AT&T startup screen?

 

[pkcable]

Probably not easily, I would just go with it, IF it was me.