In case of linux, please open the terminal and goto the AssetExplorer Home\bin directory and execute sh changedbserver.sh command which will open up the dialog box to verify the username and password for the SQL server. Please ensure that the connection is established using the TEST button and save the settings. If you get a login failed message, please reset the password for the respective login provided for the database and also ensure that the authentication used for the database is a SQL Server authentication and not windows authentication.
Regards,
Bhaskar.