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To edit a report, I would recommend:
 - Opening the report you want to edit. 
- Save it under a different name. 
- Use the report builder to make the changes. 
You can refer to the database documentation for an overview of database tables. This can be found in the Reports tab > Database documentation. 
 
If you are proficient in SQL language, you can also edit the report directly in SQL Server Management Studio (SSMS)
 
Note: check out our Report library, the report you are looking for, or close to it, might already be available