That is controlled by your League in Fulltime, they can
prevent teams from changing this, particularly relevant when Leagues have to
set Kick off times due to the availability of Referees and they wish to prevent
teams arbitrarily changing times which'll screw up the Referee planning. Also it can only be the home team that can edit a kick off time if allowed.
Grassroots Technology Support Hub
That is controlled by your League in Fulltime, they can prevent teams from changing this, particularly relevant when Leagues have to set Kick off times due to the availability of Referees and they wish to prevent teams arbitrarily changing times which'll screw up the Referee planning. Also it can only be the home team that can edit a kick off time if allowed.