How can I retrieve a user name and password? Someone installed the drupal 8 site and did not share the password. I do not know what email he has used to install the site either.
I do not have the password. 
In phpmyadmin, I clicked the database name. I ran the sql

UPDATE users SET pass = MD5( 'NewPassword' ) WHERE uid = 1;
Select * from users. 



  1146 - Table 'xxx.users' doesn't exist


How can I retrieve the drupal 8 website password?
Drupal does not store passwords, but rather password hashes. There is no way to recover the password. You can use Drush to either set a new password or generate a one-time log-in link:


Reset PW: drush upwd &lt;username&gt; --password="&lt;password&gt;"
One-time login-in link: drush uli &lt;username&gt;