Change my id back to jkbf1215@yahoo.com. messed it up by mistake. can't even now get into my yahoo personals ?

by mistake, change my personal ID, Not knowing that I would lose my old ID that i have had forever, can't get into my personal yahoo profile up and running. Will lose contact from my friends that have my old address and won't be able to contact me. help, I need to get it changed back. How do I do this fast.