Use dropdown value as parameter for other Looker Studio visualizations

Question

I have a BigQuery data source that contains a list of dates. I would like to populate a drop-down control with this list. By default, it uses a selection value of "Latest" and I've updated my various queries to handle translating this to the appropriate date.

Just as I could have a date range picker on my report from which I can select a start and end date and use the @DS_START_DATE and @DS_END_DATE parameters in a custom BigQuery data source, I would like to be able to select a date from my dropdown and use that value in a custom parameter in these other custom BigQuery data sources.

Question - Populating the parameter with the drop-down control

I specify the data source "dropdown-datasource" (a view in BigQuery) for the control and select the Date field as the control field ordering by another field. In the style tab, I indicate that this allows only a single selection and that "select all" isn't an option.

On this "dropdown-datasource", I've specified a parameter named "DateParam" with the identifier "dateparam". While the parameter shows up at the bottom of the control setup tab, it's not clear how it ever gets populated. While I can select this parameter as the control field, I get an error that there's no defined list of permitted values.

How can I populate the "dateparam" parameter with the selected value from my drop-down control?

I appreciate your help!