checkbox values from localstorage when editing form

I have stored values from a html-form to localstorage and I get the data back from localstorage to form for editing. Checked checkbox values (MaterialName) are stored to localstorage as a array. Original checkbox values are coming from database via ajax. What do I need to do to get those values in localstorage match values from database, and to be checked again when editing form? Or is it even possible this way?

// localstorage value
{
  "FormID": 150,
  "CreateDate": "2019-09-17T00:00:00",
  "FormFiller": "JOkuMuu",
  "CustomerName": "Wsoy",
  "CustomerContact": "Masa",
  "WorkName": "Lajitelmapakkaus",
  "ReadyToDate": "2019-09-19T00:00:00",
  "Instructions": "Tarkasta kirjat ",
  "Amount": 50,
  "MaterialName": "Xpohja,Tarra"
}

This is function to get all materials from database:

function addMaterials(material) {
                $MaterialName.append('<input type="checkbox" value="' + material.MaterialName + '">' + material.MaterialName + ' </input>');
            }
            $.ajax({
                type: 'GET',
                url: '/api/materials',
                dataType: 'json',
                success: function (materials) {
                    $.each(materials, function (i, material) {
                        addMaterials(material);
                    });
                },
                error: function () {
                    alert: ('Virhe ladattaessa')
                }
            });

This is function I tried to get checked values to be re-checked:

$(function () {
                    //bring data from localStorage
                    var lsdata = JSON.parse(localStorage.getItem('key'));
                    //put data to form
                    $('#formid').val(lsdata.FormID);
                    $('#createdate').val(lsdata.CreateDate);
                    $('#formfiller').val(lsdata.FormFiller);
                    $('#customerlist').empty().append(lsdata.CustomerName.split(',').map(c => new Option(c, c)));
                    $('#contact').val(lsdata.CustomerContact);
                    $('#worklist').empty().append(lsdata.WorkName.split(',').map(c => new Option(c, c)));
                    $('#readytodate').val(lsdata.ReadyToDate);
                    $('#instructions').val(lsdata.Instructions);
                    $('#amount').val(lsdata.Amount);
                    $('#materiallist').append('<input type="checkbox" checked>' + lsdata.MaterialName + ' </input>');

Everything else is working except MaterialName. It is adding new value with Xpohja,Tarra. I want it to add 'checked' to those Xpohja and Tarra, not new value.