Adjust plug fitting (5)
I believe the answer is:
adapt
'adjust' is the definition.
(synonyms)
'plug fitting' is the wordplay.
'plug' becomes 'ad' (as in plugging a product).
'fitting' becomes 'apt' (both mean appropriate).
'ad'+'apt'='ADAPT'
(Other definitions for adapt that I've seen before include "Fashion" , "Adjust (to new condition)" , "Make fit" , "Change to suit new circumstances" , "Make suitable for new purpose" .)