Unable to Block Apps on Tivo Box

One of kids could access Rakuten from apps page at top of home screen and content we think is not suitable. I was unable to block the app, the instructions are supposedly this:
Help & Settings> Parental Controls> enter PIN, and select Lock Apps & Games. Highlight the app you want to lock and press OK on the remote. Confirm by selecting Use these settings

There are 2 apps already blocked or locked when I navigate to that page but no option to block other apps, no menu to view other apps to block, no option to amend what is there, pressing right or left takes me out of menu, up or down does nothing. Tried going to the Rakuten app and long press ok as read this can work but just takes me into the app. Raised complaint with VM who replied with instructions how to lock channels or hide adult channels, not apps. Does anyone have a solution to this?