Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
I can't answer that without knowing why you couldn't just re-enter the original one in the first place.
Can you log on to the original one via a web browser? Try going to play.google.com and signing in via the original account - does it work? Can you add the original as a second email address? Remember that any contacts/apps you've added since the event are associated to the new account rather than the original one, so you'll need to do some more transferring or re-installing if you switch your main account (you should still be able to use the original one for email with the phone with no trouble).