To remove a database from a replication group, use the following command:

./bin/yugabyted xcluster remove_database_from_replication \
    --databases <comma_separated_database_names> \
    --replication_id <replication_id> \
    --target_address <ip_of_any_target_cluster_node>

./bin/yb-admin \
-master_addresses <primary_master_addresses> \
remove_namespace_from_xcluster_replication <replication_group_id> <namespace_name> <standby_master_addresses>

You should see output similar to the following:

Successfully removed db2 from xCluster Replication group repl_group1