Quick Move TM
No pokemon currently has more than two quick moves it can learn. It seems unlikely TM give access to legacy moves. Do we know if, when you use a TM, you can reroll the move you had before?
Consider a steel wing dragonite. Assuming the TM can't give it Dragon breath, then does a quick move TM automatically give it Dragon tail? Could it get steel wing again? Could it actually get breath? Do we not know yet?
Answers
Saw a Reddit thread and someone asked this to the Niantic guy that was answering questions. It seemed like you always got the other quick move on the reroll (so you can't get the one you have currently)... but who knows, Niantic may add more quick moves for each min in the update so there won't be a guarantee
essentially this^^^
If your current quick move is legacy then it will be a 50/50 change when its rolled into the new move pool.
If you have a current quick move then you will roll to the other one.
so a iron tail tyranitar will automatically get Bite. but a dragon breath dragonite will get the choice of steal wing or dragon tail.