This is just a quick tip. I was working on several forms that all had Nintex Mobile layouts. For several of these forms I used Preview mode so I could test the form, but not publish the changes to the user.
To preview a form, select the Preview button on the Nintex Forms Design Ribbon. The preview settings dialog will appear before the preview is displayed. Then choose the device type of Nintex Mobile App. Forms designed for the Nintex Mobile App are not available for preview directly within the Nintex Forms Designer as it cannot render an accurate preview. When a mobile layout is specified as the device layout to preview, the platform and mode are not longer relevant.
This worked great without issue until I realized later that I had a couple of previews left over and wondered why they didn't go away after I published the form. I couldn't find anything in the designer to remove the Mobile App previews. I forgot this simple note in the Forms User Guide:
Once the Generate Preview button is clicked the form will be made available on Nintex Mobile only for the user who has designed the form. The form will be removed from the forms list once it has been submitted. An existing preview form will be overwritten if a new preview is generated.
So I submitted the preview form, and it was gone just like it said. Silly of me to look around for 20 minutes for a delete button.
Hope this helps someone else!