Example HistoryID attribute:
<Report ID="INSERT REPORT ID HERE" HistoryID="2018-05-11T22:54:10"/>
The HistoryID is specific to report snapshots. It accepts a DateTime value in the format:
The HistoryID of available snapshots can be pulled from the REPORTSNAPSHOT table. A simple select script will get you what you need:
select * from dbo.REPORTSNAPSHOT
A HistoryID column exists in the table and the values within that column will already be in the DateTime format above.
A snapshot of a report can be created under Analysis > Report explorer in CRM.
Supplying a HistoryID value makes it display the snapshot of the report based on the provided HistoryID value.