I use is free redirection plugin. If you are using Yoast SEO premium, redirection feature is available for you already. You can also use any other plugin if you like. The only thing you need to ensure is, it should be a 301 redirection.
For this example, I’m using Redirection plugin.
Here is the scenario:
Already published post with URL: https://WPSutra.com/how-to-add-google-amp-to-wordpress-to-speed-up-your-mobile-site
New URL After editing the post slug: https://WPSutra.com/Google-amp-WordPress
Go to Tools > Redirection (or redirection tab of any other plugin that you are using). You can also set redirection using the .htaccess method.
Here you can set the 301 redirect from old post to the new one as shown in below screenshot:
What this would do is, when someone will click on your old URL, they will be automatically redirected to new URL. This would ensure you wouldn’t lose any traffic after changing post slug of the already published post.
Do note that you would lose your social media shares number & that is a very little trade-off you need to make when dealing with editing old post URL. I usually do this for editing my old blog posts or dealing with non-performing blog posts.