Singing flier forgetting day for launch again (7)
I believe the answer is:
restart
'launch again' is the definition.
(restart can mean to launch again)
'singing flier forgetting day' is the wordplay.
'singing flier' becomes 'redstart' (type of songbird).
'forgetting' is a deletion indicator.
'day' becomes 'd' (abbreviation for day).
'redstart' with 'd' taken out is 'RESTART'.
'for' is the link.
(Other definitions for restart that I've seen before include "Commence again" , "Jumping the gun will mean" , "Begin anew" , "launch again" , "begin afresh" .)