The only way to do this if you have no access to your old phone number would be to turn this off.
To turn off 2FA sign in with the recovery code so at the login select "can't sign in with the code" link. You'll then be asked for the recovery code.
When you signed up to 2FA you were given a recovery code so if you didn't make a note of it then check the email you were also sent.
Help can be found here on how to turn this off and/or change your number including using your online account manager to do this however I believe you would need access to the original number to do this:
https://www.sky.com/help/home/sky-yahoo-mail/two-step-verif/articles/two-step-verification
You will be sent a 6 digit code to use to turn this off.
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