Marlin Question changing an axis

So I have an MKS GEN L board that was on my 3d printer. The x axis has a studder in it. The problem is in that axis on the board itself(maybe just a cold solder joint in the connector). I know how to set dual axis to use 2 x motors, bUT can someone please tell me how to map the x axis to the e1 or e0 motor driver. I am not doing dual endstops at this point so I am wiring the motors in series. I only need 3 drivers for now and want to use that board.

The pins are defined in one of the pins files in Marlin/src/pins/. There are entries for X and E0, so you can just swap the values of those and it will treat E0 as X.

Thank you so much!