In the Classic interface, you were able to drag and drop Salesforce reports or Excel as Middleware file to your templates. The same can still be done in LEDD
1 - Navigate to your DocGen Package and go to the Documents tab
2 - Go to the template that you would like to associate your Salesforce report/Excel as Middleware with and click "Edit" from the arrow
3 - Navigate down to the "Connected Data" section. Select "Salesforce Reports" if you're looking to connect to a Salesforce report. Select "Named Ranges from Excel Template" if you're looking to do Excel as Middleware. Select the file/report you wish to use.
4 - Give an alias if you're using a Salesforce report. You can also add a filter parameter
5 - Enter in the range name that you've used for your Excel file if you're using Excel as middleware
6 - Hit Save!
For Excel as Middleware, in order for the Excel file to appear, you will need to have the Excel template included as part of the DocGen Package.