How to reset brake shoes?

The pistons in the wheel cylinder probably came out of the bore slightly and got cocked to one side. Otherwise the return springs should have brought the shoes back to their proper position. If you have no leaks, just push the pistons and seals back into the cylinder bore, make sure the dust boots are still where they should be, center the shoes, and slide the drums back on. If the cylinders are used and leaking fluid, I'd hone them and install a overhaul new kit.