It's over; be seated (3)
I believe the answer is:
sit
'be seated' is the definition.
(I've seen this before)
'it's over' is the wordplay.
'it's' becomes ''tis' (I've seen this before).
'over' says the letters should be written backwards.
'tis' in reverse letter order is 'SIT'.
(Other definitions for sit that I've seen before include "Pose for painter" , "Take (an examination)" , "as magistrates do" , "I sell badly the cotton yarn" , "Order dog to behave" .)