As we have changed the working model of BI Connector from version 4.0. This is a one-time process and moving forward you can use the same workbook in the future releases.
You can follow the below workaround,
Open your existing Power BI workbook.
Click on “Edit Queries” icon from the Home menu.
In the Power Query Editor, select each table that you have loaded and click on the “Advanced Editor” icon from the Home menu.
You’ll see something similar to the below Power Query.
Change the "Source" in first line to “BIConnector.Contents("<your DSN name>")” and click on “Done”.
Do this for all the tables once it is loaded successfully.