How do you shift back and forth from primary to secondary e mail address at Yahoo after opening secons e mail?

After opening up a secondary but new e-mail address in Yahoo, I found that my primary address is nowhere to be found. I tried to edit and then could see my original e mail address and the checked off primary and clicked finish but now stuck on this new address. Anyone know how to shift back abd forth from one e mail account to the other. Cannot find original account.