services.AddAntiforgery(o => o.HeaderName = "XSRF-TOKEN");
services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
services.AddSession();
services.AddMemoryCache();

<script type="text/javascript">
    $(function updateRow () {
        $.get('/FinalApprovalLetter/').done(function () {

                $('#success').append([message returned from JsonResult OnGet]);
            });
        });
    });
</script>

<input type="button" class="d-print-none" value="Set Final Date For Course (today)" onclick="updateRow" />
   <br />
    <label id="success" />

public JsonResult OnGet()
{
  //DO database row update, insert today's date in FinalApprovalDate field
  //DETERMINE AND RETURN SUCCESS/FAILURE (records affected)
  //I HAVE CODE TO DO THIS AND IT WILL WORK

    return new JsonResult("[success/failure message");
}