Setter absorbed by objective to improve! (5)
I believe the answer is:
emend
'improve' is the definition.
(emending is a kind of improving)
'setter absorbed by objective' is the wordplay.
'setter' becomes 'me' (the setter of the clue).
'absorbed by' indicates putting letters inside.
'objective' becomes 'end' (I've seen this before).
'me' put within 'end' is 'EMEND'.
'to' is the link.
(Other definitions for emend that I've seen before include "Improve by editing" , "Make correction in written material" , "Remove faults from" , "Improve (writing)" , "Make improvements or corrections" .)