Rectify when you change gear (7)
I believe the answer is:
redress
'rectify' is the definition.
(thesaurus)
'you change gear' is the wordplay.
'you change' becomes 're' (I can't justify this - if you can you should give a lot more credence to this answer).
'gear' becomes 'dress' (both can mean clothing).
're'+'dress'='REDRESS'
'when' acts as a link.
Can you help me to learn more?
(Other definitions for redress that I've seen before include "Reparation" , "Compensate" , "Set right - compensation" , "remedy" , "set straight again" .)