To allow Leaders* to edit service plans online, go to the Web Terminal pane inside of MSP and click the “Web Terminal settings…” button. In this dialog, click on the Administrators heading on the left and choose a Leader you wish to give the ability to edit service plans. Click on the “Privileges:” row, and make sure the “Edit service plans” privilege is checked.
Once logged in, a Leader can go to the Admin view in the Web Terminal by clicking on their name in the upper right corner and selecting "Switch to Admin View". In the Schedules pane of the Admin view, the Leader can click on the date containing the service they wish to edit. From here, the Leader can click on the date and time of a service to bring up the service plan dialog.
From this dialog, the Leader will be able to edit the service plan.
*Leaders are only available in the Plus Edition of MSP.