How can I make a select the value of a field in the Data Store

I have a repeat region with select boxed for Category & Sub Category.
When the Sub Category is selected, it runs a flow which adds the prodID, cat, sub_cat, mup, to the data store.
Now what I am trying to achieve is if someone has to come off the page then the selected value for cat & sub_cat is got from the Data Store.

I’ve tried as the selected value in the select:

updates.data.cat.where(prodID, prodID, ‘==’)

&

updates.data[0].cat.where(prodID, prodID, ‘==’)

but this has not worked.

Would anyone have any idea how or if this can even be done?