弄 (nòng): A highly versatile verb that means “to do,” “to make,” “to handle,” or “to manage.” Think of it as a general-purpose action word.
错 (cuò): This character simply means “wrong,” “mistaken,” or “error.”
了 (le): A grammatical particle that indicates a completed action or a change of state.
When combined, 弄 (to handle) + 错 (wrong) + 了 (completed) creates the meaning “(someone) has handled it incorrectly,” or more naturally, “to have made a mistake.”