You need to stop the application and initiate reinitializeDB.bat from [ServiceDesk Home\Server] of the command prompt, this will drop all the tables.
Also if the database is PGSQL, then initiate initPgsql.bat from the command prompt of ServiceDesk under [ServiceDesk Home\Bin].
Also if the database is PGSQL, then initiate initPgsql.bat from the command prompt of ServiceDesk under [ServiceDesk Home\Bin].