1. Login into https://portal.office.com then choose Outlook
2. On the top-right pane, you may see the Setting icon. Click on it then choose "View All Outlook Settings"
3. Setting box will appear. Choose General > Distribution groups
4. Locate the DL you want to modify under Distribution groups you own and double click on it to open it. Click membership.
5. To add a user to the distribution list, click the plus icon.
6. Type the name of the person you want to add and then click the magnifying glass to search. Then click the plus icon next to their name to add them to the Members field. Repeat with any additional people you want to add.
9. Click Save to save your changes. You're done adding members!
10. To remove a user from the distribution list, click on the name you want to remove. Then click the minus icon.
11. Click Save to save your changes. You're done removing members!