ToME: the Tales of Maj'Eyal

I bought the game on Steam and when I want to register I get I "username and email already taken". Is there any way to connect my account with Steam?

1) Log in at https://te4.org/
2) Navigate to My Profile on the menu on the right side of the website
3) Navigate to the Steam tab
4) You will be asked to log in and authorize through Steam, if I recall correctly, it has been a long while for me

I hope this helps