Adding a report to the dashboard is the same concept as adding a widget as per our help documentation (https://techdocs.broadcom.com/us/en/vmware-tanzu/cloudhealth/tanzu-cloudhealth/saas/tnz-cloudhealth/getting-started-with-tanzu-cloudhealth-getting-started-with-cloudhealth-dashboards.html)
To do so, edit the dashboard and drag the report widget onto the layout.
You can then select a report.