using System;

public class Program

{

    public static void Main()

    {

        string cdsOrgUri = "https://someinstance.crm.dynamics.com/CITTest";

        string relativePathToOdata = "/api/data/v9.1/";

        Uri uri = new Uri(new Uri(cdsOrgUri), relativePathToOdata);

        Console.WriteLine(uri);

        Console.WriteLine("^ Notice that it chops off the 'CITTest' from the original OrgUri");

    }

}