Default [Q] Note 3 Stock ROM and restore

I apologize if this question is not in proper category. I had a replacement Note 3 shipped to me from T Mobile a few days ago, and I have been having trouble. I did not root it. I was trying to see if there was a software update and it told me they were not available as it had been modified. Again, I did not do anything to the phone to change anything. I checked and it said it was custom.

So, I am wondering if anyone can direct me to where I can get a copy of the Stock software for TMobile and a link as to how to do it properly as I do not want a bill for the entire phone. And I was told there was something called Triangle Away that I would need to use to remove the Custom label. Could I just use that without restoring?

Much thanks