Hi Aakash - I assume from your question you mean how to refund a "transaction" (not translation) 
Vantiv has a few different payment platforms as you may be know, so the answer depends on the platform you are integrating to. Do you happen to know the platform? Vantiv has core platforms that large retailers use (via ISO 8583 or 610), an eCommerce platform (referred to as Litle or Lowell) for eCommerce developers, and integrated platforms (MercuryPay and Element) mostly used for card present point of sale - it can definitely get confusing! If you can point out the platform though that would help me get you a better answer.
Assuming it is the eCommerce platform (one of the easier platforms to integrate with) there are some code examples that show how to refund a customer. We refer to a refund on this platform as a "Credit" in our API - A .NET / C# code example is here - SDK Credit . Vantiv tends to deal with large retailers and while we have an API, many developers code directly to our XML spec so you could also code your own solution in .NET generating and parsing XML sent and received to our endpoint. Feel free to reach out to me directly and I can get you in touch with an expert if need be. Thanks!
