Change one's tune in second song (9)
I believe the answer is:
backtrack
'change one's tune in' is the definition.
I can't tell whether this defines the answer.
'second song' is the wordplay.
'second' becomes 'back' (to second a motion is to back it).
'song' becomes 'track' (I've seen this before).
'back'+'track'='BACKTRACK'
Can you help me to learn more?
(Other definitions for backtrack that I've seen before include "Reverse (opinion)" , "Retrace one's steps" , "Reverse one's decision" , "Return, retract" , "Withdraw" .)