Pocket knife broken – Extremely loose

Hello! If this isn't something that's okay to post, I'm happy to delete it.

I literally don't remember how, but this knife is missing a couple of pieces, one having a clip on it, and now it's extremely loose. Like, I learned about it because it came open in my pocket and poked me in the leg.

Trying to figure out what I need to do to fix it and what the replacement parts would be called? Replacement is not an option, unfortunately, it's passed down from my recently deceased grandfather.

Thank you in advance for any assistance!