How can I have stable link for a form so that when I make updates the same link can be used?

You can get the form's direct link in the Publish section. Click the "Publish" menu and then go to the "Quick Share" section where you'll see the direct link of the form.

If you updated this form using the Form Builder, the same link will still work.

Hope that helps. If you have any questions, let us know. Thank you.