Sign in to the you eBay account by supplying your account details, but instead of being asked to enter your password you will be asked to insert your Fido key;

Insert you Fido2 key into an available USB port,  Select "Security key", then click ;

At the prompt "Security Key PIN", enter the PIN code, then click . 

(in the case of a Fido key with a fingerprint reader you will need to swipe your finger on the key);

You will now be asked to touch the Fido2 key (in the case of a Fido key with a fingerprint reader you will need to swipe your finger on the key);

Once you have touched the key you will then be logged in to your eBay account.