how can i convert form to app

Unfortunately it is not possible to convert a form into a downloadable app. Although you can still add the form to your phone's homescreen. Simply follow this guide to learn how: How to Add Websites to the Home Screen on Any Smartphone or Tablet.

If you want to create an app, I have found several website that can help you create an app:

http://phonegap.com/

http://www.appsgeyser.com/create-url-app/

http://www.appypie.com/

Do let us know if you need further assistance.
Regards.