You will need to get into the parametric level of the control:
From the Main Menu press F7-Parms, F1-Setup, F1-Level
When it asks for Validation Code type PROTO3 enter
Then, at Access Level, type another 3
When you press the 2nd 3, more buttons will appear.
Be VERY careful what you change while you are in Level 3, you can change things that can damage the machine or cause problems even getting it to boot-up.
When you get to Level 3, go to F4-Axis, arrow down to BACKLASH, press F1-Edit change the values for the X axis and the Y axis to zero.
Escape back to the Main Menu.
Mount a tenth's reading indicator on the table with the tip on the side of the spindle. Use the handwheel to find the high spot, and zero the indicator.
Go to Jog, do NOT use handwheel to check backlash. Set the distance to 1 inch, jog away from the spindle 1 inch and jog back. Re-zero the indicator. Repeat the jog away and back moves until the indicator repeats to zero. Now jog the head up 1 inch, jog the table under the spindle 1 inch, jog back, and then jog the spindle back down the 1 inch. The reading on your indicator is the actual backlash at that point.
Escape back to the Main Menu, go to F7-Parms, F1-Setup, F1-Level, F4-Axis, arrow down to BACKLASH, press F1-Edit change the values for the axis to the value you just determined, escape back to the Main Menu, go to Jog and then repeat the process to verify that you have the correct backlash compensation. Make whatever adjustments are necessary.
Now repeat the whole process for the other axis.