To manually delete an index history:
On the Projects tab, go to Projects > Your Project > Indexing > History tab.
Click the delete icon () for the index to delete.
Click OK to confirm the deletion.
If the index file itself has not been deleted, you can either keep the event history but delete the index file, or delete both.
If the index files have already been deleted or the indexing task was cancelled, but the event history entry has not been deleted, then the delete applies only to the event history.