Removed Email Address by Mistake

I had a secondar email that I've had for years. I got a new computer and was trying to set up my email client, outlook. I couldn't get that email to work. I logged in to webmail and I must have mistakenly removed that email address from my account. I need to get that back but can't figure out how to do it or find a live chat to help. I use that email address for login to a few things and need access to it.