If you are an admin of a distribution group that exists in Office 365 (not in the on premise Exchange), you can edit the group memberships via the Outlook Web App:
- Log into https://outlook.office.com
- Click on the gear icon in the upper right hand corner of the page
- Search for the word distribution and click on the the one result of Distribution groups
- Select the group you want to edit from the ‘Distribution groups I own’ section
- Use the menu options (plus symbol, pencil and garbage can icons) to edit the membership
Call the Service Desk at 425.564.4357 if you would assistance with this.