As mentioned in the comments already, verify that you can connect to the database from Microsoft SQL Server Management Studio or from Visual Studio.
If you can't, review the user created in SQL Server.
This video shows how to create a user in SQL Server, in your case, you should connect with the account "sa" and change the password for the existing user, but the video gives you an idea of how to access the users in SQL Server.
If you are in a development environment, you can change the password of the CM user and after update the config to ensure both are the same.
If you don't have the credentials for connect with 'sa' account, double check with the DBA team and confirm that user/pwd is correct.