How and where to insert a custom script in the body of the form source codes?

I have to add a script to a jotform

A jotform rep said the only way I can do this is by copying the source code and manually altering the code from there..

The script that i must add to the "body" section of source code is this:

<script type="text/javascript" src="//cdn.callrail.com/companies/910482544/8a456617158cadb74b3e/12/swap.js"></script>

My question is.... Where is the body of the source code? I need to add it and I have tried adding to about 20 places and it is still not triggering the script. 

The body tag wraps the entire form element. At the bottom, add the script before the closing </body> tag. See screenshot:

See if that works. Would you also mind explaining the use of the script? I understand it's a call tracking script, but aside on that, I don't know what the script will do when placed in the form source codes.