Start again with Frenchman on top (5)
I believe the answer is:
renew
'start again' is the definition.
(to renew something is to start it again)
'with frenchman on top' is the wordplay.
'with' becomes 'w' (short for with).
'frenchman' becomes 'rene' (common French name).
'on top' means one lot of letters go next to another (in a down clue, some letters go above others).
'w' put after 'rene' is 'RENEW'.
(Other definitions for renew that I've seen before include "Restore to original state" , "Regenerate" , "Extend eg library loan" , "Invigorate" , "Extend (subscription)" .)