Configure the database to work with the apps built with the bit project templates.

Connection String
You can change connection string at appsettings.json file in Server project.
If you have selected 'Other' for the database parameter while building the project, install appropriate EntityFrameworkCore package for your intended database such as PostgreSQL, and then in the Server\Startup\Services.cs file, perform the relevant settings for the related package in the services.AddDbContext section.
Set Server as the Startup Project in solution explorer and also set it as the Default Project in Package Manager Console and run the following commands:
Add-Migration InitialMigration -OutputDir Data\Migrations -Context AppDbContext
Update-Database -Context AppDbContext

Note: If you encounter any problem in running these commands, first make sure that the solution builds successfully.

Or open a terminal in your Server project directory and run followings:
dotnet ef migrations add InitialMigration --context AppDbContext --output-dir Data/Migrations
dotnet ef database update --context AppDbContext