Agree expert can go round church by day (6)
I believe the answer is:
accede
'agree' is the definition.
(acceding is a kind of agreeing)
'expert can go round church by day' is the wordplay.
'expert' becomes 'ace' (ace is a kind of expert**).
'can go round' indicates putting letters inside.
'church' becomes 'ce' (abbreviation for Church of England).
'by' is a charade indicator (letters next to each other).
'day' becomes 'd'.
'ce'+'d'='ced'
'ace' going around 'ced' is 'ACCEDE'.
(Other definitions for accede that I've seen before include "Agree - take the throne" , "Yield" , "Agree to what is proposed" , "'Acquiesce, defer (6)'" , "Succeed to or allow" .)