To link your account, open game settings - "Link". Choose e-mail. Switch to fold "Registration", enter your e-mail address, pick a password and then press "Ok". You will receive e-mail for registration confirmation. Follow a link to finish registration.
In the game, enter your e-mail address and password, and then press "Ok". Done!
Remember that sending a message could take from several minutes to 24 hours. If you didn't receive the letter during 24 hours, please, contact technical support of the game. Don't forget to check Spam folder before writing.