UPDATE admin_user SET `password` = CONCAT(SHA2('xxxxxxxxNewPassword', 256), ':xxxxxxxx:1') WHERE `username` = 'admin';

xxxxxxxx
could be any characters, any length, just make sure the two parts are the same
NewPassword
is the new password
If you get error after reset the password
You did not sign in correctly or your account is temporarily disabled.
check the lock_expires filed of the user