Remove all the indices and let them rebuild:
1. Go to the ITSS host
2. Open command prompt as an administrator
3. Run: net stop elasticsearch-service-x64 /Y
4. Go to the folder C:\Program Files\Quest\IT Security Search\ElasticSearch\elasticsearch\data
5. Delete ITSecirutySearch folder permanently
6. Got to the folder C:\Program Files\Quest\IT Security Search\ElasticSearch\elasticsearch\logs
7. Delete all files from there
8. Open Administrator command line
9. Run the command: net start itss.server
10. Go to the ITSS settings | ER connector and check that the index is in the process of rebuilding