Since you’ve asked about the Couchbase Backup Service in other posts, if this question is about creating a repository in the Backup Service, please see Create repository - #2 by hyunjuV and the documentation https://docs.couchbase.com/server/current/manage/manage-backup-and-restore/manage-backup-and-restore.html
If your question is about setting up backup in Couchbase Autonomous Operator (CAO), then, please see the CAO documentation on that topic – https://docs.couchbase.com/operator/current/concept-backup.html