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
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