Yahoo provides you an option to Recover My Yahoo Account, if you forget your user’s credentials like email id or password or you forget the security questions, anything else. If you forget what security question you select, then you can simply get it via navigating into the settings section. If you are unable to recover your account, then you should check your user’s credentials as well your internet connection. You can also talk to help desk to resolve it.
https://www.my-lenovosupport.com/yahoo-customer-support-number/