To add or remove a user from a distribution list or Office 365 group, please follow the steps below
Login to the O365 portal.
In the left-hand pane, under Recipients click Groups.
Select the group type your group is under from either Microsoft 365, Distribution list, Mail-enabled security or Dynamic distribution list.
Click on the group and then click the Members tab.
Click View all and manage members.
Click Add members.
Tip: To remove an existing user:
Tick the box next to their name.
Click the 3 horizontal dots.
Click Remove the user or users.