How do you re-download airdrop. I seem to have deleted it.

Check Finder Preferences. See if AirDrop is enabled in the sidebar. If it is, toggle it and try again.

Restart your Mac, and see if that clears this.

Restart into Safe Mode, and try again. This rebuilds caches, and disables some common add-ons.

If that doesn’t work, post again, and I’ll post some info for retrieving and posting the system config.

Config info re-posted sans serial number:

AirDrop isn’t something that can be deleted. Not easily.

Which MacBook Air year, which version of macOS, why do you think it’s deleted, and what have you tried?

Here are set-up details, and the prerequisite hardware and software versions:

Use AirDrop on your Mac - Apple Support.

Good that it’s working.

Any Mac running Sierra can be upgraded to High Sierra. I’d upgrade at least that far.

Your Mac is new enough for Mojave (last version with 32- and 64-bit app support), and for Catalina, and for the current Big Sur.

How to get old versions of macOS - Apple Support

In Finder->Preferences->Sidebar make sure AirDrop is selected.