How to change URL structure

Hi,
I’ve created a page lets call it https://www.xxx.com/yyy.
To the page yyy I’ve linked another page, lets call it zzz.
I want the url to be https://www.xxx.com/yyy/zzz, but instead it is https://www.xxx.com/yyyzzz.

I’ve tried to change it with the permalink option but it will not take the change. I’ve also tried to download the Simple URL’s plugin but it doesn’t find any URL’s at all.

Does anyone know how to change the URL structure so it will be how I want it???
Thanks! ??