You need to edit the report that is displayed in this web part. The steps are by memory and I do not a have a ServiceDesk handy at the moment so there might be small discrepancies but it should give you an idea what to look for.
To see or change the report shown:
- Site Actions > Edit Page
- Site Actions > Modify Page
- Edit icon on the web part
By defaults, the report used in that web part should be: Reports > Default > My Requests
When you want to modify it, I would recommend cloning the default report, doing necessary editing on the clone and then change the Report web part on the page to use your modified report.