Editing Group Membership of M365 Group

Find and select the group on the left-hand column under the "Groups" heading.

Then in the Ribbon Bar click on "Group Settings" then choose "Edit Group"

From this screen you can Add users from the "add people" field and remove members by hovering over their name and clicking the red "x".

On the left side of the window Choose "Groups" or "More Apps" > "Groups". Then choose "Credit Card Participants" then click on "Members"

 

From this window you can remove members and if you want to add a member select "Add members" from the ribbon bar.