New Module Form field that filters based upon other field selection

Hi everyone. I am creating a new module and a form for my users to fill out.

I put a select list on the form of Thirdparties. I also want a field for the user to choose the Contact.

But I want to filter the Contact list to only show the Contacts that belong to the currently selected Thirdparty.

For instance… Suppose I have the following 3rd parties with contacts.

Apple
John
Mary

Google
Mark
David
Sally

If the user selects Apple, I want them to only see the Contacts of John and Mary in my Contact list.

If the users selects Google, I want them to only see the Contacts of Mark, David, Sally in the list.

Thanks for the help.