How can update custom meta for all posts

How can update custom meta (likes) for all posts that have this meta?

If you want to update every post that has this meta:

See the returns field parameter and custom field parameters for Wp_Query to 1) retrieve only posts with that meta_key, and 2) to lighten query and only return the ids instead of full objects. Then loop through them.

Something like this (untested):

$args = array( 'fields'          => 'ids', 
               'posts_per_page'  => -1, 
               'post_type'       => 'posts', 
               'meta_key'        => 'likes' 
               );
$all_ids = new WP_Query( $args );

foreach( $all_ids as $ai ) {

   update_post_meta( $ai->post->ID, 'likes', 1 );
}
wp_reset_postdata();