Do forgive and have done with it! (3)
I believe the answer is:
con
'do' is the definition.
(both can mean to defraud)
'forgive and have done with it' is the wordplay.
I cannot really see how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is found in the answer.
The remaining letters 'co' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for con that I've seen before include "Fleece" , "Study - trick" , "Swindle in draconian way" , "do something?" , "Informally swindle" .)