How can I change the thank you link on my form?

My last question is: If I want link customers to the form via a button - I've created one here: https://littlebluelife.com/trial-page/

How can I send them back to my site following registration?

Yes, you may change the thank you page and redirect your users to a different page instead of showing the thank you message, the following guide will help you doing so: https://www.jotform.com/help/38-Redirecting-Users-to-a-Different-Page 

If you have more questions, please let us know.