Go back to a former state (7)
I believe the answer is:
regress
'go back to a former state' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for regress that I've seen before include "Decline" , "Go back to earlier state, perhaps of health" , "Return or revert" , "Go back to a lower level" , "Return to a former or less developed state" .)