Just adjust my reel (6)
I believe the answer is:
'just' is the definition.
(I know that just can be written as merely)
'adjust my reel' is the wordplay.
'adjust' indicates anagramming the letters.
'myreel' is an anagram of 'MERELY'.
(Other definitions for merely that I've seen before include "Simply - only" , "'Only, and nothing more (6)'" , "Just one" .)