For the ones that have been sent to the old one already the only way is for you to send them one at a time to the new one.

In addition, you might do this.

To notify your contacts of the email change click on OPTION…MAIL OPTIONS…go to the left side and click on ACCOUNTS..then click on ADD OR EDIT…go back and click on MAIL again…Under MANAGEMENT scroll down and click on ANNOUNCE EMAIL ADDRESS…once you are done with what you
want the notice to say AND after adding your contactlist in the header click on PREVIEW AND SEND….when the new screen comes up and everything is as you want it…go below and send it….

Just log in to your old email account and forward all emails to your new yahoo id.this is the only one way to get your emails in new yahoo id from old one.