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.
I would like to recommend you to check the following article to get the idea about the Tumblr sidebar editing.
You will need to edit your template HTML to inject the form code.
Here is an example where the form code is added after the buttons section in sidebar.
I used the following code:
<Form Script Code Here>
You can try to edit your sidebar in the same way.
Alternatively, it is possible to create a separate form page, and link it to the sidebar. See the following thread:
If you need any further assistance, please let us know.