And he swims in to land when you give assistance (4,1,4)
I believe the answer is:
lend a hand
'give assistance' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for lend a hand that I've seen before include "Turn to and help" , "Provide help" , "Pitch in" , "Give assistance" , "temporarily transfer an employee" .)