I can't delete pinterest

What exactly do you mean by "march's reserve copy"? Was this a beta pre-release? If so, there is likely a profile associated with it you may need to delete first: Settings app > General > Profiles & Device Management.

I'm not sure I understand the reserved copy reference either. If holding down on the icon on the iPad to get the app icon to wiggle doesn't work, try deleting the app in Settings>General>Storage & iCloud Usage>Storage>Manage Storage. Let the list of apps load. Find Pinterest and tap on it. Delete it in the next screen.