Try once more, sing away in practising for performance (6)
I believe the answer is:
rehear
'try once more' is the definition.
('hear' can be a synonym for 'try' so perhaps 'rehear' is OK for 'try once more')
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for rehear that I've seen before include "Try again (in court)" , "be a sympathetic listener, not for the first time" , "Hold the trial again." , "Retry (a lawsuit)" .)