You can use both in one application, because there’s no real direct interface between the two.
You build your DRF project just like you would build any other DRF project.
You build your Channels application just like you would build any other Channels application.
If your Channels application needs to call a function from your DRF project, then the Channels consumer would import that function and call it - just like it could call any other function.
Just keep in mind that your Channels application has no reason to call a DRF View.