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.
If you received a letter, followed a link and saw such text "You have specified incorrect information about the following email account. The link may also have expired." - it means that while registration you pressed "Ok" button several times and several letters were sent to you. Wait for the last letter and follow the link. Also remember that you need to confirm a registration within 24 hours after receiving a letter. Otherwise the link will be expired.