Sorry if this has been covered but I was curious how I log into my multiple WoW accounts using the same Battle.Net login?

I was about to merge my other two WoW accounts under my main account (which I've already merged under Battle.net) and it said I'd be using my e-mail to login but thats the email i use to login to my main account. How would I get to the other WoW accounts then?

Thanks.