Hi there,
You would need to add custom fields to your posts/pages. A plugin like ACF might help with that.
Then you can do this:
add_action( 'wp_head', function() {
if ( is_singular() ) {
$meta_title = get_post_meta( get_the_ID(), 'your_meta_title_custom_field', true );
$meta_desc = get_post_meta( get_the_ID(), 'your_meta_description_custom_field', true );
if ( $meta_title ) {
printf( '<meta name="title" content="%s">', $meta_title );
}
if ( $meta_desc ) {
printf( '<meta name="description" content="%s">', $meta_desc );
}
}
} );