The following has been tested on a Cloud9 server with the following versions:
If phpMyAdmin is not already installed, use the following command to install phpMyAdmin on your server:
phpmyadmin-ctl install
mysql-ctl start
The first command displays the username. Use it to connect to /myservername/phpmyadmin/ or /localhost/phpmyadmin/. Leave the password field empty:

Once you are connected, in the users tab, click on Edit Privileges for the user you just created.
Scroll down to Change password and create a new password. After password change, you have to log out
and log in again.