Point your browser to https://help.yahoo.com/kb/account to start. Click or tap the orange "Cannot access your account?" Button to start the recovery process. Yahoo will then ask if you know your account name, recovery email address, or phone number. You should be able to start the process by entering your account name even if you don't know the other information.
Depending on a few different variables related to the configuration of your account, you should be able to answer the prompts and get a new password even if you are missing information. Once you are in your Yahoo account with the new password, select the Account Settings option and then answer the prompt to change your password to a new one and set your phone number correctly.
First of all, go to the account recovery page of Yahoo mail that is https://login.yahoo.com/forgot . This process is same for mobile and desktop. Now enter your Yahoo mail address into the given box and then click on Continue. Now click on Yes, send me an Account Key tab.