Cooperate to operate a muppet from inside (4,2)
I believe the answer is:
team up
'cooperate' is the definition.
(thesaurus)
'operate a muppet from inside' is the wordplay.
'inside' indicates the answer is hidden within the clue.
'TEAM UP' is hidden within 'operate a muppet from'.
'to' is the link.
(Other definitions for team up that I've seen before include "Brighton and Hove Albion following promotion?" , "Join" , "Couple" , "Unite for a common goal" .)