Can't update to one ui 7 even through the beta. When I try to software update it it says what 24 hrs and try again. I got this phone on the carrier att and switched to tmobile.
Even though your phone is carrier unlocked, it's looking for an update from AT&T, which it won't find on T-Mobile. If you can borrow an AT&T SIM from someone, that would be the fastest way to get the update.
For a more permanent solution, you'll need to go to an authorized service center and have them update the phone's firmware. Here's where you can find locations:
