Have a look at this
https://kellenmace.com/remove-custom-post-type-slug-from-permalinks/
I use it with this plugin: Code Snippets By Shea Bunge
This allows you to modify your functions.php file without having to directly edit it. This means WordPress core and theme updates won’t remove your changes.
Finally, may I suggest you try using a staging plugin to make a development version of your site so that you don’t have to try things out on the live site.
Try this: WP Staging – DB & File Duplicator & Migration By WP-Staging
I hope that helps.
Warmly
Steve