What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Unfortunately, you can't do that in the form builder. You will have to manually do it by getting the form source codes and inserting your favicon tag.
After adding the favicon tag, you will have to save the source codes as an HTML file then upload it to your own server then get the file URL to publish the form.