Hello,
Which website are you trying to sign into?
A passkey can be stored in several different places, so just because you cannot find it on your computer doesn't necessarily mean it is gone/orphaned. It may have been saved on another device, such as your phone, or in a password manager.
Here are a few places to check.
If you're using Windows 11:
Go to Settings > Accounts > Passkeys.
This will show passkeys saved locally on your computer. You can search for this website and see if it is lsited.
If you're using Microsoft Edge:
Open Edge > Settings > Passwords and autofill > Microsoft Password Manager. Once again, you can search for this website.
If you're using Google Chrome:
Open Chrome > Settings > Passwords and autofill > Google Password Manager.
You may also want to check your phone if you have previously used it to sign into that website.
If you cannot find the passkey anywhere, look for an option such as "Try another way" on the website's sign-in screen. If you can sign in using your password or another verification method, you should be able to go into your account security settings to remove the old passkey and register a new one, if the website supports this.