approved I-130

Sorry to ask this question again. I've got an approved I-130. It was approved last year, but some how I lost the notice. What is the step I need to do next? File I-485?

I asked this question to USCIS, they told me to file Application for Action on an Approved Application or Petition (I-824), I check the purpose of this, and it says:

To request a duplicate approval notice, to request approval notice to another U.S. Consulate, and to request notice to a U.S. Consulate for derivative visas to family members.

Why do I need a duplicate approval notice anyway?

Thanks for any information!