自分の間違いを

one's own mistake(s)

→ 自分
phrase Rare #28,586
one's own mistake(s) 自分の means “one's own,” 間違い means “mistake,” and を marks the phrase as the object of a verb. The exact person referred to by 自分 depends on context.
JA: まずは自分の間違いを認めましょう。
EN: First, let's admit our own mistake.

彼女はあっさり自分の間違いを認める必要はなかったのに

She didn’t have to readily admit her mistake.

トム自分の間違いを認めた

Tom admitted his mistake.

自分の間違いを認めろよ

Admit that you were wrong.

彼女は自分の間違いを我々に隠そうとした

She tried to hide her mistake from us.

自分の間違いを自分で直した

I corrected my own mistake.