Change my gmail address to my Apple ID

So I had a Apple ID but I changed it because I could not remember what it was or maybe I typed it in wrong so I created a new one using my gmail account email address but now I want to change it back to what it originally was so when I go to appleid.Apple.com website and it asked me to change my Apple ID how do I change my gmail address that I have now created as my Apple ID back to my @icloud Apple ID?