show validation message on button click

Question

$.ajax({

url: '@Url.Action("AddNewBranch", "BranchAPI", new { httproute = "" })',

type: "POST",

data: JSON.stringify(branchDetail),

contentType: "application/json;charset=utf-8",

success: function (result) {

if (result == "Success") {

addNewBranchModal();

}

else if (result == "fail") {

alert("2nd");                      //after this i want to enable @Html.ValidationMessageFor                                             

};

},

error: function (e) {

alert(e);

}