EurekaLog Viewer comes with ready to use FireBird database (see also: DB mode vs View mode).
Default location for database is %APPDATA%\Neos Eureka S.r.l\EurekaLog\Viewer\Eureka.fdb file. For example: C:\Users\UserName\AppData\Roaming\Neos Eureka S.r.l\EurekaLog\Viewer\Eureka.fdb
The default database account for the database itself is:
DB login: SYSDBA
DB password: masterkey
The default EurekaLog account on this database is:
EurekaLog login: admin
EurekaLog password: admin
You can change database account by using any database managing tool, that supports FireBird databases.
You can change EurekaLog account by using usual configure user's accounts command.
If you forgot EurekaLog's account (and you do know the database's one) - then you can use any database tool to reset password manually. Contact EurekaLog's support on this issue.
If you forgot database's account - then you lose your database. You can reinstall EurekaLog to get clean copy of default FireBird's database (make sure to delete old database to ensure installation of a new copy).
Please note, that not all database modes supports user's accounts.