Go backward (7)
'go backward' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for reverse that I've seen before include "Move backwards" , "Do u-turn to reserve" , "Countermand" , "Britannia's place" , "Travel backwards" .)
(Other definitions for regress that I've seen before include "return journey" , "Return to former life" , "Lapse" , "Decline" , "Deteriorate" .)