Add 19% Vat only for companies

Hey guys,

I have a one-page checkout (https://reform-der-grundsteuer.de/produkte/grundsteuererklaerung-unbebautes-grundstueck/) and my clients can be private individuals or businesses.

Currently I charge €686, but the price should be only for private individuals. If someone fills out the field ?Company (optional) I want to add 19% VAT

How can I implement that?

Would be happy if someone can help me!

The page I need help with: [log in to see the link]