1. For Manual Installation (Install in a custom position )
Search the keyword '<!--pifyform-start-->' in your page code which installed the form.
And then remove the form code between '<!--pifyform-start-->' and ''<!--pifyform-end-->''.
2. For Automatic installation
Go to Publish->Mange Instsallations, then click 'Remove'.
If the app has been uninstalled, you could reinstall the app, and then do that.
3. Contact support
Welcome to contact our support to get assistance. We are willing to help for you. Contact Us now.