lets see, if i remember right, you have to write a letter, and send copies to
1 your store manager
2 the manager of the store you want to go to
3 the union
the letter should say why you want the transfer . always say, closer to home, it's the only thing they care about. NEVER say, it's because of problems where you are. they will never let you go.
It's always best, to  have talked to both the manager, and possible dept head of where you want to go, ahead of time, so they can go to bat for you, and say '" yes we need/ want you"
sometimes, it's easy to get transfered, sometimes, flat impossible.
but, it can take a while, at least a couple of weeks