Cant save after change value field with javasciprt ?

I have problem , i try for change value in field in xml make java sciprt, this new screen,

why after save this cant save to database ?.
 

async function addQtyku() {

    var scale = document.getElementById("ctl00_phF_form_CstPXTextEdit2");

    var qty = document.getElementById("ctl00_phG_CstFormView177_CstQtyNbr123");

    console.log(qty);

    var floatValue = parseFloat(scale.textContent);

    qty.val = floatValue.toFixed(2);

    qty.value = floatValue.toFixed(2);

    qty.setValue(floatValue.toFixed(2));

    qty.dispatchEvent(new Event('change'));

    console.log(qty);

  }

Please Help Me Sense
Thanks