How do I show the WP admin error page?

wp_die() See the codex for full usage details:

https://codex.wordpress.org/Function_Reference/wp_die

You can even include html in the message field if you want to.

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