Cause the ruin of (2,3)
(Other definitions for do for that I've seen before include "suit" , "Destroy or kill" , "Ruin" .)
'cause the ruin of' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for undo that I've seen before include "Ruin or loose" , "Unfasten, loosen" , "Ruin, destroy" , "Open button or ruin" , "Open or unfasten" .)