Rewe delivery service - how can you choose time slots?

Somehow I do not see through how I can choose the time window for delivery.

I'm on the page where the lists for the time slots are there, but somehow I can look as I want, it simply does not select anything. Neither from the cell phone nor from the laptop.

Maybe someone can help me and explain where I have to click?

The page is overloaded. The time slots are fully booked. That's why you can't choose anything.

Okay thanks