Pop back and fold suit (5)
I believe the answer is:
apply
'suit' is the definition.
(I've seen this before)
'pop back and fold' is the wordplay.
'pop' becomes 'pa' (both can mean father).
'back' is a reversal indicator.
'and' means one lot of letters go next to another.
'fold' becomes 'ply' (I've seen this before).
'pa' in reverse letter order is 'ap'.
'ap'+'ply'='APPLY'
(Other definitions for apply that I've seen before include "Make a formal request (to someone); put on" , "Send off (form, etc)" , "Employ; be relevant" , "Make use of" , "Administer" .)