Add extra data to analysis server cube connection in imported Powerpivot model

I imported a Excel with Power Pivot model in Power BI and it works as expected. The model has Excel files and an Analysis Services  Cube as data sources.

However when i want to add an extra data field form the cube i don't get a list of the available fields in the cube. The only way seems to be through MDX.

Is it possible to get through to the Cube and the dimensions and measures?