Aurelia - how to change a date-picker value with pure JS (from outside the Aurelia Framework)

I'm building automation function to fill in the form in Aurelia framework app. I'm doing it from outside the framework (pure JS). I can change the "input" field value and everything works fine. But I don't know how to change the [date-range-picker] value. When I change the "input" value of this date-range-picker field - everything is OK on the screen but the date is not set (when I click the field -the popup datepicker shows default date).