Hi @Krithica G _EXTERNAL_ ~ it depends how your users are added to that group. Are you using Crowd? Active Directory? One option that you can use directly in Confluence is to navigate to the Groups screen and click the trash icon next to the ones you want to remove (https://yoursite/admin/users/domembersofgroupsearch.action?membersOfGroupTerm=confluence-users). Not really bulk delete, but it would be pretty quick....
Another option may be to use the API: https://docs.atlassian.com/ConfluenceServer/rest/8.9.0/#api/admin/user
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