If you’re trying to accomplish this in C# (RestSharp specifically) it would look something like this…

var fileBytes = File.ReadAllBytes(@"C:\myprofile.ovpn");
var request = new RestRequest("ovpn/client/upload");
request.AddHeader("Authorization", _authToken);
request.AddFile("file", fileBytes, "myprofile.ovpn");
var response = _restClient.Post<BaseResponse>(request);