Submit Button returns an "https://" instead of "http://" causing DNS error

I added a payment form w/ a paypal/credit card html code. The submit button returns a message that my info was submitted. However, the "Back" to payment form button returns a DNS error message. I noticed, that it is re-directing me to an "https://" url address instead of my website's which is an "http://" url address. the URL address are similar except it is "https://" instead of "http://". How can I fix it so my customers will not get annoyed and frustrated?