Alter plug fitting (6)
'alter' is the definition.
(thesaurus)
'plug fitting' is the wordplay.
'plug' becomes 'ad' (Advertisement plugs products).
'fitting' becomes 'just' ('just' can be similar in meaning to 'fitting').
'ad'+'just'='ADJUST'
(Other definitions for adjust that I've seen before include "Adapt, fix" , "Modify - tweak" , "Tune" , "Alter, adapt" , "Make small changes" .)
(Other definitions for adapt that I've seen before include "Change to suit a new purpose" , "Adjust (to new conditions)" , "match" , "Become adjusted to new conditions" , "Alter, amend" .)