Work free; undo (6)
I believe the answer is:
loosen
This clue is a double definition.
'work free' is the first definition.
(I've seen this before)
'undo' is the second definition.
(I've seen this in another clue)
(Other definitions for loosen that I've seen before include "Make less tight, slacken" , "Relax the tension" , "relax or tear apart" , "Work free" , "Undo a little" .)