Tango has appeal as exercise (4)
I believe the answer is:
task
'exercise' is the definition.
(I've seen this before)
'tango has appeal' is the wordplay.
'tango' becomes 'T' (phonetic alphabet: alpha, bravo, charlie etc.).
'has' is a charade indicator (letters next to each other).
'appeal' becomes 'ask' (I've seen this in other clues).
't'+'ask'='TASK'
'as' is the link.
(Other definitions for task that I've seen before include "Job to be done" , "Burden with work" , "Job, undertaking" , "Chore, job." , "something to do" .)