"The Apollo System Username and Apollo System Password fields allow you to specify the credentials for an existing user that will be used as a "system" user in certain background operations and other processing that requires admin level privileges.
Apollo system username/password was added to configuration wizard originally for Windows authentication or LDAP authentication.
For Windows authentication or LDAP authentication, you are not setting the password for a user in this step, you are supplying the credentials for an existing user in the chosen authentication system, that has the esp_administrator role.
For APOLLO authentication, you may specify a new user and password in the Configuration Wizard, but you will need to establish those credentials using Data Manager > Configuration > Users, the first time Data Manager is run and before you begin adding data to your catalog."
If you run the configuration wizard and change both system username and password to something other than admin/apollo123, either one or two more steps are needed. Initially you will need to log into DM using admin/apollo123 because this is the default value set in the principals table. In the DM > Configuration > Users section, add the new user name with administrator role and set the password the same as the system user password.
If you run the configuration wizard and leave the DM admin username (i.e., "admin") unchanged, and just change the admin user password (e.g., "apollo123456"). After the configuration wizard, you still need to login to DM using admin/apollo123. Then change the password for admin user in the DM > Configuration > Users > admin, so that admin password match your new password during configuration wizard. So it will be easier just change it in DM later instead of in configuration wizard, of course once your changed the password of admin user, you need to match the changed password during configuration wizard if you decide to run configuration wizard again.