The following may be what you need. The negative value tells Marlin the endstop is -13mm from 0 of the bed.
In configuration.h:
// Travel limits after homing (units are in mm)
#define X_MIN_POS -13
#define Y_MIN_POS 0
#define Z_MIN_POS 0
In configuration.h:
// Travel limits after homing (units are in mm)
#define X_MIN_POS -13
#define Y_MIN_POS 0
#define Z_MIN_POS 0