Rank Math has a long tutorial on how to edit meta titles and descriptions. Here: https://rankmath.com/kb/editing-seo-meta-at-scale/
It's very long and probably time consuming, so If you don't have a lot of time you can try our latest free WordPress plugin called Orbisius SEO Editor.
You just need to select Rank Math plugin from the Source SEO Plugin's dropdown and then decide what to bulk edit meta titles, descriptions or both
You can also export and import in CSV.
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