When forms installed are no longer needed.  There are three ways to remove a form even you have uninstalled the app.

1. Remove the form manually

Search the keyword '<!--pifyform-start-->' in the page code which installed the form. 

And then remove the form code between '<!--pifyform-start-->' and ''<!--pifyform-end-->''.

2. Remove the form in app

If the form was installed by Automatically  in the app You could reinstall the app, and then go to Publish->Mange Instsallations, then click 'Remove'.

3. Contact support

Welcome to contact our support to get assistance. We are willing to help for you. Contact Us now.