How do I make an existing email into my extra email address?

I have two emails on Yahoo! and I want to merge them, is that possible? Please help!
How do I make an existing email into my extra email address?
If you have Yahoo! Mail Plus you can contact Yahoo! customer support and request a merge, or you can setup auto-forward feature (only available in Mail Plus) on your second e-mail to send all e-mails to first address.