To edit a Matter, click Settings -> Edit.
That will take you to the Matter settings page. On the Matter settings page, Matter owners can change Matter general info like description, status, type, source, etc.
They can manage external Contacts that are involved with a Matter, but also manage members from inside a company that are working together on this Matter and set their default billing rates.
Matter members can see all this data, but they can’t edit it, with the exception that they can set up a default billing rate for themselves on that Matter.
To see more about Matter settings page, go to: Matter settings page