Hi Karthik,
Yes "db" is your SID , in this case seems to be "TST".
You can also do that extend from DBACockpit -> Database <SID> tab -> Spacen -> Database -> click on your <SID> you'll see the "Extend DB Space" available
You might also be interested about the auto-extend functionnality: Configuring Automatic Database Space Expansion in SAP Adaptive Server Enterprise
Best regards,
Victoria.