Agree it's put on back to front (3)
I believe the answer is:
nod
'agree' is the definition.
(I've seen this before)
'put on back to front' is the wordplay.
'put on' becomes 'don' ('don' can be a synonym of 'put on').
'back to front' says the letters should be written in reverse.
'don' reversed gives 'NOD'.
'it's' is the link.
(Other definitions for nod that I've seen before include "OT land" , "slight bow" , "Land of exile" , "sleepy land" , "Asleep in the land" .)