To modify the reference account mappings within a template (new experience), do the following:
How to update RA budget reports?
Go to Maintenance > Planning Templates > Template Setup.
Choose the desired template and click Setup > Template Setup.
On the Template Setup page, locate the specific line you want to change.
Click the edit icon in column J and select Reference Account to open the mapping screen.
On the Reference Account Mapping screen, you can add a new row using the Add Row button or edit an existing mapping.
After making your changes, click Keep Changes and Close to save and exit the mapping screen
Click Save.