Default [Q] cannot roll back to 8.0

I'm a noob to windows phones and this is driving me insane.
Thanks for all the help in advance! Hoping to get this solved this evening.

Now I'm trying to see if I can flash something on it to make it run on T-mobile LTE not just H or H+
I'm on the Singapore rm-875 and 8.0 and obviously a bit clueless