Add or delete users in Microsoft SharePoint Online
Add users
If you have an existing group configured, to add users to it:
In your site, click Site Contents, and then click Settings.
Under "Users and Permissions", click People and groups.
On the left, select the group to which you'd like to add the users.
Click the drop-down arrow next to New, and then select Add Users.
In the box "Enter names, email addresses or 'Everyone'", type the name, username, or email address of the user and select them from the search box that appears.
Include a personal message if desired, and click Show Options to choose whether to send an email invitation.
When you're finished, click Share.
Delete users
To delete users from a SharePoint site:
In your site, click Site Contents, and then click Settings.
Under "Users and Permissions", click People and groups.
On the left, select the group from which you'd like to remove the users.
Use the checkboxes to select the users you want to delete.
Click Actions, and then select Remove Users from Group.
Click OK to confirm the deletion.