Put back in controls head of state ultimately sought (8)
I believe the answer is:
reinsert
'put back in' is the definition.
(insert for a second time)
'controls head of state ultimately sought' is the wordplay.
'controls' becomes 'reins' (rein is a kind of control).
'head of state' becomes 'ER' (abbreviation for Elizabeth Regina).
'ultimately' indicates one should take the final letters.
The final letter of 'sought' is 't'.
'reins'+'er'+'t'='REINSERT'
(Other definitions for reinsert that I've seen before include "Enter, sir! (anag) - put in again" , "plant back" , "Put back in" .)