When a session is closed, no further actions can be taken from the Plan for the lines associated with it.
When no action is suggested in the Side Panel for a line in your Plan, it is likely because the corresponding session has been closed.
As a reminder, sessions should only be closed when you are certain you will not return to them (i.e., when the final cost, attendance, etc., have been entered) since no further action is possible in the Plan for lines linked to a closed session.
To edit a line linked to a closed session, you will need to reopen the relevant session from Sessions.