Update formxml and formjson in systemform D365

Question

I need to update Form from C# I try to Update with classic methode but any things updated

        Entity form = new Entity("systemform");
        form.Id = new Guid(listView1.SelectedItems[0].SubItems[4].Text);
        form["formxml"] = System.IO.File.ReadAllText(@"C:\Users\seatmane\source\repos\getFromsMethodes\getFromsMethodes\formXML.xml");
        form["formjson"] = System.IO.File.ReadAllText(@"C:\Users\seatmane\source\repos\getFromsMethodes\getFromsMethodes\formJSON.json");
        Service.Update(form);