apply_filters ( 'jetpack_relatedposts_filter_exclude_post_ids', array $args[’exclude_post_ids’], string $post_id )

Notes

In the following example, 1037 and 1038 are the IDs of the posts we want to exclude:

function jetpackme_exclude_related_post( $exclude_post_ids, $post_id ) {
    // $post_id is the post we are currently getting related posts for
    $exclude_post_ids[] = 1037; // Exclude post_id 1037
    $exclude_post_ids[] = 1038; // Also exclude post_id 1038
    return $exclude_post_ids;
}
add_filter( 'jetpack_relatedposts_filter_exclude_post_ids', 'jetpackme_exclude_related_post', 20, 2 );