Calm down, seeing volunteers back in position (7)
I believe the answer is:
placate
'calm down' is the definition.
(placating is a kind of calming down)
'volunteers back in position' is the wordplay.
'volunteers' becomes 'ta' (abbreviation for Territorial Army).
'back' is a reversal indicator.
'in' means one lot of letters goes inside another.
'position' becomes 'place' ('place' can be a synonym of 'position'**).
'ta' in reverse letter order is 'at'.
'at' put into 'place' is 'PLACATE'.
'seeing' acts as a link.
(Other definitions for placate that I've seen before include "Make calm, conciliate" , "'Pacify, appease (7)'" , "Mollify, soothe anger" , "Make less angry" , "Mollify, appease" .)