automated balance increment

I bought a theme (pricerr , fiverr clone theme)
I want to customize it.
My plan is like below
” When user pay thru paypal or other payment gateways, their balance in website automatically increase.”

There alredy is a function which allows admin to increase user’s balance (in admin panel)
But i want to make it automated
(user pays with payment gateway ->automated balance increment)

I am not programmer so i cant touch the code.(if it is easy let me know how)

Is there any plugin that perfoms automated action?

Thanks for reading