Change phone number associated with syncup watch.

Due a system error when i got my daughters watch (609), i had to return the original one and get a new line (640) and watch. I returned the original watch and tmobile accidentally cancelled the new line (640) associated with the working watch. They were able to connect the working watch to the original line (609) but the app still has the 640 line associated with the watch and I need the 609 line connected to the account. Will unpairing and repairing work?