Can’t override slug for a non-existing page

I’m working on this WordPress website and I had the menu structured as follows

https://www.domain.com/subdomain/
-> https://www.domain.com/subdomain/contact
-> https://www.domain.com/subdomain/about-us

Now I accidentally renamed the slug for https://www.domain.com/subdomain/ to https://www.domain.com/subdomain/home/

And I have no idea how to change this back.

The page https://www.domain.com/subdomain/ is now non-existent and redirecting to the home page. I tried to do create a new page and name that /subdomain/ but instead it names it /subdomain-2/

The funny thing is, the sub-pages still work as intended..