Bidding for a change in Thebes (6)
I believe the answer is:
behest
'bidding' is the definition.
(behest is a kind of bidding)
'change in thebes' is the wordplay.
'change in' indicates anagramming the letters.
'thebes' is an anagram of 'BEHEST'.
'for a' is the link.
(Other definitions for behest that I've seen before include "Order" , "(At someone's) command" , "Command - Thebes (anag)" , "Command, bidding" .)