Revert to regular galleries

I’m not sure what you mean, it doesn’t override the WP gallery at all. If you need to move your images you’ll have to add the same images but using the WP gallery functionality

I have a website with hundreds of posts and Easy Image Gallery under each one of them. I want to automatically convert those galleries to normal WordPress [gallery]s.

Not without running some SQL queries (or manually doing it).

Easy Image Gallery stores each attachment ID in a comma separated list with a meta_key of _easy_image_gallery, against the post ID.

Have a look at how WordPress stores their galleries and then write a SQL query to move them.

Thanks ??

No problem, good luck!