Assumptions:

1. UCS is deployed in HA (ContactServer & ContactServer_B)

 Steps: 

1. Stop both UCS
2. Rename the existing Index directory (for example D:\GCTI\ContactServer_Index to D:\GCTI\ContactServer_Index_bak\)
3. Add a new folder D:\GCTI\ContactServer_IndexNew
4. configure index.srl-->index-rebuild = 'if-new' in Application ContactServer
5. Start 'ContactServer' application as Primary (this will start builing the index for this UCS)
6. Start 'ContactServer_B' application as backup