"Restore from a backup (the /opt/IBM/ITM/tables directory)" is the best option, but that's not always an option. These steps will remove ALL data in the TEMS, HOWEVER, you don't have to reinstall all of the application support; you need to re-apply it, but you don't need to reinstall it. Here are the steps that I went through with ITM 6.2.1 IF2 on 32-bit Red Hat:
1. stop the TEMS and all other agents on the box.
2. remove the /opt/IBM/ITM/tables/YOUR_TEMS_NAME directory
3. uninstall the TEMS component by running /opt/IBM/ITM/bin/uninstall.sh and only select the TEMS component.
4. run the install from the CD/DVD and choose to install the TEMS
5. The install will create a directory named /opt/IBM/ITM/todata. Rename this directory to "YOUR_TEMS_NAME".
6. run 'itmcmd -S -t YOUR_TEMS_NAME ms' to configure the TEMS
7. restart the TeMS and all other agents
8. open up the "Manage Tivoli Monitoring Services" and add all application support (it's all still installed; you just need to re-apply it to the TEMS)
IMO, the reinstall (or re-configure) should recreate the /opt/IBM/ITM/tables/YOUR_TEMS_NAME directory, but it doesn't (it creates the directory, but not the EIB files). So the whole trick is copying the "todata" folder.