When you are creating your project with angular cli, you can use ng newcommand. It generates all your components with predefined sass files.
ng new My_New_Project --style=sass
But if you are changing your existing style in your project then use ng set command:
ng set defaults.styleExt scss
If you like this question & answer and want to contribute, then write your question & answer and email to freewebmentor[@]gmail.com. Your question and answer will appear on FreeWebMentor.com and help other developers.