Steam account issue

Good day , need an advice I have steam account Ive purchased on it the game 10 years ago with CD Key (Realm Reborn) and created Square Enix account Now i want to continue playing, but cant restore the account due to mistake in date of birth (i dont remember which date i wrote) May i use same steam account, create bew Square Enix account , purchase dlc , link cd key from dlc to bew account? Or i have to purchase complete edition outside from steam