Login with Apple ID

It is now possible to login to the Zus app with Apple ID, so I did. And it works. I thought it would be possible to change the emailaddress of my old account, so I can connect it with Apple ID, but that looks like it’s impossible.
So I remove all devices from my old account, and will add them to my Apple ID account. And then will add all devices I have, only three so that shouldn’t be too much of a hassle. It should be made simpler though.
My old account will not be used anymore, but I don’t see how I can delete it. Please help how to do this.

One issue left: in the Zus app, going to profile, is redirected to the website. And he website doesn’t have login with Apple ID, only FB. When will this be the case?

With kind regards, Henk.