It's been a while since I worked for Walgreeens, but when I did I asked for a transfer (they didn't have one at the time but I did see the process). I would definitely start with your current DM; for one, they might happen to know the DM in the area you want to transfer and could give you a good word. Also, you don't want it to look like you're going behind their back. Then, I'd reach out to the DM in the new area and see what they have/if they can keep you in mind for openings.