Often due to companies security policy you have to deactivate the SYSTEM user in the HANA database. Follow the below procedure to lock the system user.
Login to tenant db using hdbsql
hdbsql -i instance nr -n dbhost:sqlport -u username -p mypassword
Login with user having the privilege USER ADMIN and execute the below command
hdbsql=> ALTER USER SYSTEM DEACTIVATE USER NOW;
Syntax to lock any user ALTER USER <username> DEACTIVATE USER NOW;