For a noted purpose, you can do this for yourself (4)
I believe the answer is:
fend
'you can do this for yourself' is the definition.
The definition suggests a singular noun which matches the answer.
'for a noted purpose' is the wordplay.
I cannot really understand how this works, but
'purpose' could be 'end' (both can mean a goal) and 'end' is present in the answer.
A single letter 'f' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for fend that I've seen before include "Ward off from offender" , "Manage (usually for oneself)" , "Ward (off); manage (for oneself)" , "Try to manage without help" .)