How can i add a Norwegian Zip Code Lookup in Form?

Hey,

Thanks for a beautiful plugin!

I have a question, one of our competitors (https://xn--strmdeals-n8a.no/)
Is using CF7.

On their form you can type in a Norwegian zip code (4 numbers) and the city of the zip code will automatically appear next to the input field.

Could you please guide me in the right direction to how to pull this off?

Thank you!