Return the key to the wrong person (7)
I believe the answer is:
respond
'return' is the definition.
(thesaurus)
'the key to the wrong person' is the wordplay.
'the key' becomes 'd' (I've seen this in other clues**).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'the wrong' indicates an anagram.
'person' is an anagram of 'respon'.
'd' after 'respon' is 'RESPOND'.
(Other definitions for respond that I've seen before include "Come back" , "Answer back" , "Reply - react" , "Write back" , "React (positively) to a stimulus or treatment" .)