You should be wearing nitrile gloves when working with lens assemblies. Oils from fingerprints leave marks on the lens elements and cause major headaches during reassembly.

If you left fingerprints on a lens, you want to identify if it is plastic or glass and clean with the appropriate cleaning agent. If it is glass, use reagent grade Isopropyl alcohol + lens wipes. If plastic use a plastic friendly alcohol or cleaner. Some clear plastics become opaque with Isopropyl alcohol.

Remove the four 3.2 mm screws on the silver lens cover.