To recover your username (nickname), click on the button LOGIN and if the data is incorrect, you will see the caption "Did you forget your name or password?".
Click on the button Recover (indicated by the red arrow in the image below):
Then enter your username or e-mail (in the fields indicated by the yellow arrows in the image below):
You will receive a note in your email in-basket that will show your username.
If you do not receive it within a few minutes, please check the spam or junk mail folder.