YOU SAID:

You can do this, they don't know it's your first day!

INTO JAPANESE

あなたはこれを行うことができます、彼らは今日があなたの初日であることを知りません！

BACK INTO ENGLISH

You can do this, they won't know that today is your first day!

INTO JAPANESE

そうすれば、今日があなたの初日であることは彼らに気づかれないでしょう。

BACK INTO ENGLISH

That way, they won't know it's your first day.

INTO JAPANESE

そうすれば、今日が初日であることを相手に気づかれることはありません。

BACK INTO ENGLISH

That way, the other person won't notice that it's your first day.

INTO JAPANESE

そうすれば、相手は今日が初日であることに気づかなくなります。

BACK INTO ENGLISH

That way, the other person won't notice that it's your first day.