Directory Theme – How to Add Custom Fields to List Details

Just got the Directory Theme. When you click a listing, by default there is a “Description” and “Details” toggle section. In the “Details” section, “Website Link” and “Category” display by default.

I would like to add additional custom fields/rows to this table. For example, “Affiliate Link”, “Multi-tier” (i.e. yes/no), etc.

How would I go about doing this? Is there a setting in the admin panel? If not, how can I manually add fields?