There is no command per-se, AFAIK you have to write a routine to do this, there is the MR command that may be able to be used, or there is a Backlash Compensation routine shown in this Galil manual.
http://www.electromate.com/db_support/downloads/ManualV3.pdfI have not tried it.
Normally on a CNC machine the backlash comp is taken up in one particular direction, when a position is reached and the axis is reversed in the B.L. take up direction, the axis will move at a high rate by the amount of the recorded backlash.
Nosmo.