Assuming your question refers to Gambiet81: no take back available (as far as I know) therefore you need to use the setup function (see above tips).
This would imply a sequence such as:
Code:
Up-arrrow to enter Menu mode
'V' to enter move piece mode
revert last Gambiet's move
'V' to re-enter move piece mode
revert your own move you wanted to take back
'V' to re-enter move piece mode
enter your new move choice
'G' to let Gambiet play from the new position
instruct Gambiet to play black or white accordingly
Of course this dummy sequence is most simple, without captures. If captures occurred, you would need to place relevant pieces using the 'P' command in-between 'V' commands.
MfG,
Eric