delete_post_meta hook code example

Example: delete_post_meta

delete_post_meta( int $post_id, string $meta_key, mixed $meta_value = '' )
  
Deletes a post meta field for the given post ID.

You can match based on the key, or key and value. 
Removing based on key and value, will keep from removing duplicate metadata 
with the same key. It also allows removing all metadata matching the key, 
if needed.