Yahoo allows you to easily reset a lost password if you have access to the recovery phone number you gave them when you created the account. If you have neither, then there is one other option you can try.
The Yahoo Sign-in Helper might allow you to reset your account. It could give you a bit of hope if you otherwise fear that you’ve potentially lost all access to your email.
Recovering a Lost Yahoo Password
Point your browser to https://help.yahoo.com/kb/account to start. Click or touch the orange “Can’t access your account?” button to begin the recovery process. Yahoo will then ask you if you know your account name, recovery email address or phone number. You should be able to begin the process by entering your account name even if you don’t know the other information.
Depending on a few different variables in regards to how your account is configured, you should be able to answer the prompts and receive a new password even if you’re missing information. Once you’re in your Yahoo account with the new password, select the Account Settings option and then answer the prompt to change your password to something new as well as set your phone number properly.
If you can’t access your account in this manner and you have no access to your old phone number or recovery email, then unfortunately more than likely your account got locked. Yahoo has to do this to prevent people from gaining unlawful entry into vacant accounts.