Took one’s part and succeeded having help, not the first (5)
I believe the answer is:
sided
'took' is the definition.
(siding is a kind of taking)
'one's part and succeeded having help not the first' is the wordplay.
I cannot really understand how this works, but
'part' could be 'side' (side is a kind of part) and 'side' is located in the answer.
A single letter 'd' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sided that I've seen before include "Took part with person in a dispute" , "Showed solidarity (with)" , "Allied oneself (with one party)" .)