Welcome to the forum. Your entertainment pass just gives you access to the content on the entertainment section of the NOW TV app/website. Al the other apps on the box are third-party apps, so to watch ITV catch-up on your laptop rather than go to NOW TV you'd go direct to the ITV Hub website and watch from there
The same applies if you want to watch BBC iPlayer, All4 etc - just go direct to their websites.
You can, but you don't do it via the NOW TV website (or the NOW TV app) you need to go direct to ITV's Hub website and watch on there.