You can SSH into your instance and find the login credential using the following command.

$ cat /home/ec2-user/credentials
////////////////////credentials info////////////////////
--- Redmine
----- User: admin
----- Password : admin
--- MySQL
----- User: root
----- Password : dEHjcVkoQQaMAJgUuMFm
----- User: redmine
----- Password : cQwulTbwBLJNPEGFPURx
////////////////////////////////////////////////////////

To access MySQL, connect to the EC2 instance either on AWS console or in your own command prompt. Login with root use and the following command:

mysql -u root -p 
Password: ****

Enter the password as found in /home/ec2-user/crednetials

Then you can list all the database:

mysql> show databases;