Can I get my iPhone 6S repaired at a apple store if I bought it at a T-Mobile?

I dropped my iPhone 6S in water and I left it in rice for 3 days, so far it's working fine but I can see the water in the screen and it gets hot quickly. I want to know if I can get it fixed by apple even though I bought it at a T-Mobile, I didn't get the warranty either.

Of course, you don't have to buy anything there, as long as its their product they will fix or answer questions.

Sure, you can.
If your phone is under the warraty, It is free to repaired