Untappd uses Foursquare for all venue information.
To add a venue, you need to create a Foursquare account, and create a venue via their Mobile App or via the web at https://foursquare.com/add-place. Once the venue has been created and you check-in into it on Foursquare - it will show up in your search in the "Add Location" screen of Untappd during check-in.
We cannot create venues in Untappd, all venues must be created in Foursquare first.
If you created the venue as a "home" private category - please make sure you follow these steps to make sure it's searchable: