How to keep newsletter box on original page after submitting form?

First and foremost, Thanks for the plugin! I am new to WordPress and find the various plugins rather helpful. Everything works great; however, I would like to keep the newsletter box open after submitting the form and simply display the thank you message at the bottom of the box. Right now it simply closes and displays the thank you text in the same place as the newsletter box. What code could I add to do that? What file would it go in? By trade I am a Java Developer and know little about PHP (although I am thinking this may be an Ajax function?)

Your thoughts are greatly appreciated.

https://www.ads-software.com/plugins/simple-newsletter-signup/