You can contact them via the email on their website. That's how I booked my experience.
It should be in your email to contact them to set that up. You also call them with your email info ready to set it up.
You can setup your account with the email you made the purchase. Once logged in, you can see the vouchers available and click redeem. You can also email or call them as Gumer mentioned and their team is great.
Thanks! Your answer is awaiting moderation.