There is a difference between the newer Microsoft Groups and the Distribution Groups.
To access the Distribution Group menu, you can login to Outlook on the web, select the Settings Cog in the top right of Outlook on the Web.
When the search option appears, search for Distribution and select the Distribution Groups option.
When selected, it will load the Distribution Groups (may take a moment) and when loaded, you can edit the Groups you own by selecting the pencil above to edit various parts of the group.
