How to recreate a missing or broken part

Hi again! Its been a long time since I last posted a tutorial. This time around, the dilemma broke out when we moved to a different place. Packing stuff and everything including Gunplas. Sad to say that when I was pack my HG 1/144 Aile Stiker pack, one ot its boosters fell and broke its fin. I looked for the broken piece but it was gone and was eaten by the "Floor monster."

So today's tutorial, involves on creating the broken fin with plastic plates.

Here's what you need.