My permalinks is set to /%post_id%/ (post id).

https://elrons.co.il/%post_id%/

I want to change them all to /%postname%/ (which is the post slug).

https://elrons.co.il/%postname%/

Problem is, whenever I change it, it gives 404 errors from my old page urls.

for example, this: https://elrons.co.il/1779/

should change to: https://elrons.co.il/pil-kahol-font/

But it gives 404 instead.

How do I make 301 redirection from /%post_id%/ to /%postname%/?