Tackle missing note in organ (3)
I believe the answer is:
ear
'organ' is the definition.
(the ear is an organ)
'tackle missing note' is the wordplay.
I cannot quite see how this works, but
'note' could be 'e' (musical note) and 'e' is located in the answer.
The remaining letters 'ar' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for ear that I've seen before include "Lug (colloq.)" , "Spike of, eg, corn" , "'Give every man thine ..., but few thy voice'/Hamlet" , "Seed-bearing spike" , "Attention; an organ" .)