How to find and reference field name on spawned page

I've been trying to find some information on how to specifically reference a field name on a spawned page. My goal is to have my "spawn button" only displayed on the last page of the document at all times. I have currently have a hidden button on my spawn template, but would like to find a way to make it visible only on the last page (which is a spawned page).

I've been playing around with this tutorial but can't figure out how to make it work for my purposes: https://wordwizardsinc.com/blog/finding-the-fieldname-prefix-on-acrobat-acroform-spawned-template-pages-using-javascript-functions/ 

Thank you!