Using JavaScript to Update the Value of a DecimalRangeField in FlaskWTForm

I have a FlaskWTForm that uses DecimalRangeFields. This is the code in Python:

class DummyForm(FlaskForm):
    field1 = DecimalRangeField('field1', [validators.DataRequired(), validators.NumberRange(min=0, max=5)], default=0) 

I'm trying to implement a button on the front end which changes the value of the DecimalRangeField. This is the basic html:

  <p>{{ dummyform.field1.label }}: <span><output for="field1" id="field1">{{ dummyform.field1.data }}</span></output></p>
  {{ dummyform.field1(step=0.1, oninput="outputUpdate(value, 'field1')") }}

  <button onclick="autoFill(3.0)">3</button>

I'm trying to add the functionality in JS. here's the javascript:

function autoFill(option) {
        document.getElementById("myForm").reset();
        document.getElementById('field1').value = option;

    }

Although this changes the value (in terms of the number displayed) that appears on the front end, it does not change the value on the slider itself. Also, when submitting the form, it does not use this updated value. All help is appreciated!