Adding and removing recipients from distribution lists is the responsibility of the distribution list owner. This owner is typically set at the creation of the distribution list. If you are not the distribution list owner, then you will not be able to add or remove recipients. If you are the owner, here's the steps you'll take to edit the list. 

1) Navigate to and log in. This will require authentication via the Microsoft MFA app on your mobile device. 

2) Click the gear icon in the upper right corner of the screen, and then click the View Outlook Settings hyperlink located towards the bottom of the Settings toolbar. 

3) Click General and then Distribution Groups to see a list of groups that you belong to and own (it may take a minute or two for anything to appear here, so be patient):

4) Under "Distribution groups I own", select the list that you wish to edit, and then click the Pencil icon in the upper left. 

4) You will be presented with a pop up window to edit the list. Click Membership on the navigation pane on the left, and click "+" to add members. You will then be presented with a search box to search the global directory for users (you can search by last name, user name, email address, etc.) One you find the person you'd like to add, click the plus button next to their name, and then click the Save button in the upper left corner of the window. 

To remove members, select the user you want to remove from the list of Members, and click the "-" button. 

Once you're done adding and removing users, click the Save button in the lower right corner of the window. This will close the window, and you're all set!