Arrange help, infant has not repeated earlier success (5,2,3,3)
I believe the answer is:
flash in the pan
'success' is the definition.
(I have seen 'Ephemeral success' mean 'flash in the pan' so perhaps 'success' could also mean 'flash in the pan')
'arrange help infant has' is the wordplay.
'arrange' indicates an anagram.
'help'+'infant'+'has'='helpinfanthas'
'helpinfanthas' is an anagram of 'FLASH IN THE PAN'.
'not repeated earlier' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for flash in the pan that I've seen before include "briefly successful thing" , "One-off success" , "Ephemeral success" , "Brilliance that doesn't last" , "Brief success - flambe moment?" .)