Fixed everything in it, as agreed (7)
I believe the answer is:
tallied
'agreed' is the definition.
('tally' can be a synonym of 'agree')
'fixed everything in it' is the wordplay.
'fixed' becomes 'tied' (tying is a kind of fixing).
'everything' becomes 'all' (I've seen this before).
'in it' means one lot of letters goes inside another.
'tied' placed around 'all' is 'TALLIED'.
'as' is the link.
(Other definitions for tallied that I've seen before include "Matched" , "Corresponded - kept score" , "Agreed, corresponded" , "Agreed; calculated" , "Reckoned debt or score" .)