Try to attract volunteers over first (7)
I believe the answer is:
attempt
'try to' is the definition.
(thesaurus)
'attract volunteers over first' is the wordplay.
'attract' becomes 'tempt' (I've seen this in other clues).
'volunteers' becomes 'ta' (abbreviation for Territorial Army).
'over' shows that the letters should be reversed in order.
'first' is a charade indicator (letters next to each other).
'ta' back-to-front is 'at'.
'tempt' put after 'at' is 'ATTEMPT'.
(Other definitions for attempt that I've seen before include "bash" , "Endeavor, try" , "Shot" , "Undertake" , "Effort; go" .)