我忘记了密码是什么。

Wǒ wàngjì le mìmǎ shì shénme.

I forgot what the password is.

我忘记了带我的手机。

Wǒ wàngjì le dài wǒ de shǒujī.

I forgot to bring my phone.

请不要忘记明天上午9:30开会。

Qǐng búyào wàngjì míngtiān shàngwǔ jiǔ diǎn sānshí fēn kāihuì.

Please do not forget we have a meeting tomorrow at 9:30am.