Navigate to the report whose properties you wish to edit, and hover over the "Settings" to find the data sources chosen. Click on it to open the report settings.
In the popup that appears, you can change the name, and data sources of the report. Data sources here are the advertising channels, the analytics sources linked to these advertising channels get included automatically.
Click "Update Report" once you're done with the changes. On saving the changes, you will receive a "Report updated successfully" alert.
Learn more about the overall structure of a report.