Couple years ago I bought two USB-A yubikeys, one lives in my keyring, another in a fireproof safe.
Time passed, now my laptop doesn't have a USB-A port anymore, and I've been using my phone more and more to access accounts that ask for the yubikey to authenticate, so I picked up a new yubikey with USB C and NFC. I figure I'll keep that one on the keychain, one in a fireproof safe near my desktop and ask my dad to keep the last one in the safe at his home.
But here's the issue: when I originally got two keys, I registered them at the same time in all accounts such as that any of the two keys work. This was over five years ago, I recall there was a QR Code or passcode of some sort I had to input the same for both keys to work with the authenticator... Is it possible to access that so I can add a third key? If not, how can I add a new key?
Also, is there some way to check what services my keys are attached to? I remember the most important stuff off the top of my head, sure, but it HAS happened before that a website I don't often use asked for a yubikey I didn't remember adding to it!