Where do I save or where is the header.component.ts file?

Where do I save or where is the header.component.ts file that mentions this part of nebular: https://akveo.github.io/nebular/docs/auth/getting-user-token#configure-token-extraction:

Use token
Okay, let's use the token to extract a payload and show username in the header. Open your header.component.ts and import the following services: