How to disable original url so that only the slug works

I have a page called “sign me up” and WordPress has created the url: https://orszco-pack.org/sign-me-up

I have entered the slug “join” so now https://orszco-pack.org/join goes to this page. I now want to disable the original url so that it doesn’t work. How do I do this?

Thanks in advance.

Simon

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