Turn or return to gallery (6)
I believe the answer is:
rotate
'turn' is the definition.
(I know that rotate is a more specific form of the action the turn)
'or return to gallery' is the wordplay.
'return' shows that the letters should be reversed in order.
'to gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
'or' written backwards gives 'ro'.
'ro'+'tate'='ROTATE'
(Other definitions for rotate that I've seen before include "Turn around on axis or central point" , "Spin as on axle" , "Spin round" , "Revolve" , "Alternate" .)