Passing If-Modified-Since in a web request request header

Question

In one of the API which I am trying to consume I am required to pass If-Modified-Since in the format of 2019-07-25T15:26:49+05:30. The Property for passing If-Modified-Since is DateTime in C#. How can we pass the parameter in the format with TimeZone into the same.

webReqeust.IfModifiedSince = DateTime.UtcNow;