How to update custom user meta field in wp?

You are using the wrong meta key:

update_user_meta( $user_id, 'Save Posts', $_POST['save_post_external'] );
update_user_meta( $user_id, 'Save Posts', $_POST['save_post_internal'] );

And that should be:

update_user_meta( $user_id, 'save_post_external', $_POST['save_post_external'] );
update_user_meta( $user_id, 'save_post_internal', $_POST['save_post_internal'] );

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)