Having served as a cleaner, finished (4,3)
I believe the answer is:
done for
'finished' is the definition.
(done for can mean doomed or finished)
'having served as a cleaner' is the wordplay.
I cannot really understand how this works, but
'a' could be 'one' and 'one' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for done for that I've seen before include "in serious trouble" , "finished" , "Ruined" , "condemned" , "killed" .)