Populate a dropdown list based on user selection of a previous dropdown list

Hi,
Great plugin!! Really simplifies a lot of things.
I was just wondering if it is possible to populate a dropdown list based on user selection of a previous dropdown list.
eg the first dropdown list shows name of countries & then depending on the country he selects populate the states, like if country is USA then american states if UK then show UK’s states.

How do i achieve this any idea?

https://www.ads-software.com/plugins/si-contact-form/