Changing Data Source from SSAS back to SQL DB

Context:

Developed a lot of reporting/BI IP in a PowerBI  file which was connected to a Azure SQL DB. Over time, we migrated towards using SSAS (SQL Cube) which contained a 1:1 copy of the same DB.

Our PowerBI file was then pointed to the cube, and we eventually migrated away. Now, we are in a position where we want to edit the data source of the file and point it back to the SQL DB, but we are unable to do so.

All of the "edit" data features are greyed out, bar Edit Queries -> Data source settings (Unfortunately this only allows us to change to another data source which has to be a SSAS source.

How can I edit the PBI file to point the data source back to the SQL DB? The tables, columns, etc are 100% the same in both the SQL DB and the cube