editing Meeting template

I can't figure out how to edit the meeting template, so that the changes will be applied to future meetings as well."

Without your club number we can do nothing for you.
Please read the documentation on Agenda
support.toastmastersclubs.org/doc/item/agenda-index

Edit the templates in the Agenda Settings Module.
Changes will not flow through to any dated agendas that have already been created from the original template.
Any dated agendas created after the template has been updated will reflect the change