I changed permalink structure but the links are not redirecting

For example my previous link used to look like this:

https://subdomain.mysite.com/category-name/subcategory-name/some-post-name

and now i changed to:

https://subdomain.mysite.com/some-post-name

The problem is that the old links do not automaticly redirect to new ones.
Any idea how to make a proper redirect? I use Nginx…