newbie question

I am new as a beta user, and I have a very basic problem: I do not have access to the beta app. Tacx sent me a message, with this information about my preferred platform (Windows TDA):

"Access to Beta can be provided through Microsoft Appcenter, after we register you as a Beta tester you will receive an email to confirm your registration in Appcenter. Subsequently, we will add you to the Windows distribution list. Afterwards, you should be able to download the latest Windows Beta build."

But I never received any information at all (certainly not a registration to) Microsoft Appcenter. I emailed Tacx with this question, but no answer.

Could anybody here tell me where you get your beta TDA?