Limit Post Revisions

Keeps only the five most recent revisions of each post, which stops the database from growing with old copies.

Code

add_filter( 'wp_revisions_to_keep', function ( $num, $post ) {
    return 5;
}, 10, 2 );

Return 0 to disable revisions or -1 to keep all. Existing extra revisions are removed the next time a post is saved.

Install WPIDE on your WordPress site (it is free) and open Code Snippets.
Use snippet above adds it from the library in one click. Or copy the code into a new snippet with the same code type.
It is added inactive: review the code and settings, then switch it on.