T%his is a new tank, so the first problem is, how did you cycle it? It is appearing that it was not fully cycled, so we need to know just how it was done.
If you are seeing nitrite--note, this is nitrite with the "i", not nitrate with "a"--this is deadly to fish, especially mollies. A major partial water change (60-70% of the tank volume) should be done immediately. Use a conditioner. If you can get Prime or Ultimate, both of these conditioners also detoxify nitrite and will help here. Do the partial water change every day until nitrite is zero (and assuming ammonia also is zero).
Fish are internally affected by ammonia and nitrite so there is no way of telling what may have been done, and if the fish will live through it or for how long. What's done is done. Good luck going forward. And welcome to TFF.