Hi Richard,
Here is the link for the queries from SAP to delete the multitenant backups
The system tables for Multitenant Database's reside under SYS_DATABASES schema under the SYSTEMDB
You need to execute the below command by connecting to SYSTEMDB using the hdbsql command:
hdbsql -i <INSTANCE_NO> -n <SERVER NAME> -d SystemDB -u <USER_NAME> -p <PASSWORD>
USER_NAME should be assigned the roles to administer the backups
(for example SYSTEM or other user defined roles)
BACKUP CATALOG DELETE FOR SID ALL BEFORE BACKUP_ID <ID of specific BACKUP> COMPLETE (or WITH FILE or WITH BACKINT)
SID= tenant database
BACKUP_ID= the ID until which the backups need to be deleted
https://help.sap.com/saphelp_hanaplatform/helpdata/en/22/275913eb9e4a5bb539fc8df3da77f1/content.htm
Hope this helps
Sunil