In CARTO Builder, table joins (as well as most data manipulation) is done through Analysis. You just have to follow these steps:
Import both datasets to your map. Remember you'll have to do import each dataset one by one! As you pointed out, only one of those has a valid geometry; the statistics dataset will display a yellow warning triangle, meaning it has no geometry and can't be plotted on the map.
Click on your dataset that does have a geometry column in it and switch to the ANALYSIS tab.
Click ADD ANALYSIS, then select the Join columns from second layer option.
Now fill in the wizard with (2) the dataset you mean to join, (3) the columns that match in both datasets, normally a name or code, and (4) the rows you want to keep from each table. When in doubt, just selct all columns from both tables.
Click APPLY... and you're done!
You can find this and more info about CARTO Builder in the CARTO Guides...
...and see the whole process in action in the following GIF:

Disclaimer: I'm currently working for CARTO's Support Team.