It’s not an app unlike in the US. You need to go to the channel section within the entertainment part of the NOW app, then you’ll find it at the a far right/bottom.
Please bear in mind that Peacock UK content lineup is just awful in comparison to the US lineup. So nothing is guaranteed to even be the same on both libraries.
For any show your trying to watch your best to download an app called JustWatch which will tell you what service if any the content your wanting to watch is on.
FYI that I do not work for NOW, just a NOW customer trying to help