Adjust payment gateway to offer free trials

I need the payment gateway API's of my website adjusted to offer free trials. My website is currently using the Listingpro Theme on WordPress, the payment gateways are part of the Theme. I need someone that is able to go into the original Theme files and make the necessary adjustment for Stripe, PayPal, and 2Checkout to offer customers free trials for the first month of their subscription.

My website is www.mycarnivalmatch.com