All you need to do is log into your account using your Apple ID and password. Your Yahoo account isn't involved unless you omitted to provide us with a critical piece of information such as you forgot your account password and are trying to reset it.
Click on this link to read what to do "If you forgot your Apple ID password" --> https://support.apple.com/HT201487
or go directly to this link --> http://iforgot.apple.com/
If you didn't receive your verification or reset email click here --> https://support.apple.com/HT201455
If you are being sent a verification code to a phone number to which you no longer have access, click on the next link to see the various ways of getting a verification code:
Get a verification code and sign in with two-factor authentication --> https://support.apple.com/HT204974
If you still need help:
Contact Apple for help with Apple ID account security "This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues." --> https://support.apple.com/HT204169
Also read about "What to do after [or before] you change your Apple ID email address or password" --> https://support.apple.com/HT204071