Sorry for how long it took saw this today. It depends on the service you are using. Most you would have to go through some sort of support for example here is dropbox - https://www.yubico.com/why-yubico/for-individuals/dropbox-for-individuals/#secret
I suggest having backup options where available I personally like one's that allow multiple Yubikeys to be registered where I can keep one safe incase other is lost. Some can use phone numbers, or google authenticator. But again varies a lot depending on what service you use it on.