そんな事忘れてしまえ。

such (about the actions of the listener, or about ideas expressed or understood by the listener); like that; that sort of

thing; matter; incident; occurrence; event; something serious; trouble; crisis; circumstances; situation; state of affairs; work; business; affair; after an inflectable word, creates a noun phrase indicating something the speaker does not feel close to; nominalizing suffix; pretending to ...; playing make-believe ...; alias; aka; nickname; alternative name; also known as

to forget; to leave carelessly; to be forgetful of; to forget about; to forget (an article)