Manually jog or move your spindle to the center of your workspace and reset to establish a (0,0,0) position
The Move the spindle with a G0 command to X=20 and Y=20 (mm).
Now issue a Zero X axis command.
The Machine should first rise to your Z safety distance setting, then move in the negative direction toward X=0. After a short move, manually operate the X limit Switch and observe if the zeroing sequence begins.
Likewise with Y.
Be ready to kill power if strange things happen