It's easy - here's how.
Create a parallel process event.
Have it set the player's x and y coordinates to variables - i.e. PlayerX and PlayerY. After that, have a wait 1 frame command, and then create a conditional branch. In the conditional, you're checking to see if the player is at the edge of the map. i.e.
@>Conditional Branch: Variable PlayerX == 0
Then run the transfer coordinates, using a transfer player event, set to the map you want, the x/y value you want(the edge) and the variable (PlayerX or PlayerY, whichever one you didn't use before.) Also, make another one for each side of the map you want transferable, changing the variable and the amount as you see fit.