Modify Content-Type value in boundary/form data

Is there any way in REST Sharp version 111.3 to modify the content-Type value inside the form data?Below is an example outgoing call I captured with Fiddler. As you can see, the content is JSON (AttributeFormat), but when I add that parameter, it's automatically adding text/plain (Bolded below)

C# Code snippit

var request new RestRequest(options)..........request.AddParameter("Arequest","{"attributeFormat":"pdf"}";

POST https://someurl.com/run HTTP/1.1

Authorization: Bearer adfafd....User-Agent: RestSharp/111.3.0.0Accept: application/json, text/json, text/x-json, text/javascript, application/xml, text/xmlHost: someurl.comAccept-Encoding: gzip, deflate, brConnection: keep-aliveContent-Type: multipart/form-data; boundary="215c45a3-b9aa-40f1-9eb5-8ceefb192370"Content-Length: 204

--215c45a3-b9aa-40f1-9eb5-8ceefb192370

Content-Disposition: form-data; name=ARequestContent-Type: text/plain; charset=utf-8

{"attributeFormat":"pdf"}

--215c45a3-b9aa-40f1-9eb5-8ceefb192370--

Thanks for any help

Tried to add a json item to the body/form, but the content-type inside the boundary keeps listing it ast text/plain instead of application/json