can I download iTunes on a MacBook Air

The iTunes app for Mac computers was discontinued and replaced when macOS Catalina was released. It cannot be installed on Macs that are running Catalina or later. See the following Apple article for information about the replacement apps: What happened to iTunes? - Apple Support

You may be able to unlock an iPhone that has a forgotten passcode by using a computer, but if you do need to use a Mac, use Finder instead of iTunes.

There is an Apple article that explains what to do if you have forgotten an iPhone or iPad passcode. Click on the following link: If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support

If that is not an option, you will need to use a computer. See: If you forgot your iPhone passcode - Apple Support

If your MacBook is running Catalina or later then iTunes no longer exists for it. What you need is already integrated into finder. Just plug your device in, click on finder, under locations your device will show there.