JAVASCRIPT

Update react final form field

<Form
  mutators={{
    // expect (field, value) args from the mutator
    setValue: ([field, value], state, { changeValue }) => {
      changeValue(state, field, () => value)
    }
  }}
  render={({ form, ...rest }) => {
    // put the reference on a window variable of your choice here
    if (!window.setFormValue) window.setFormValue = form.mutators.setValue

    return (
      <>
        <Field name="field1">...</Field>
        <Field name="field2">...</Field>
        ...
      </>
    )
  }}
/>

// somewhere else, outside of the React application

window.setFormValue('field1', 'value1')
window.setFormValue('field2', 'value2')