where is "Keychain Access"?

Applications -> Utilities -> Keychain Access

Re: 6x6, if your Apple Watch does not want to unlock your Mac, there are instructions in this forum that explain how to reset unlock with Apple Watch, and that involves the Applications -> Utilities -> Keychain Access utility, along with deleting some files.

Here is one example:

Mac not unlocking after watchOS 7 update - Apple Community

You don’t need to use Keychain Access to set that up. On your Mac, go to System Settings > Login Password and check “Use Apple Watch to unlock apps and your Mac.”