In case, you can't add the app after installation (it's not showing up), follow the instructions below to fully uninstall the app and then install it again.
- Navigate to Site Content -> Find NODE VISION - Employee Directory -> Hover over the item -> Click the three dots to display a context menu (Return to Classic SharePoint if in the modern SharePoint) -> Click Remove (see here)
- Navigate to Site Settings -> Recycle Bin -> Remove the app from the bin (either Empty Recycle Bin or select the app and delete, see here) -> Click Second-stage recycle bin link and do the same for the second-stage bin. This step is important!
- Navigate to the App Catalog -> Remove the app (see here).
- Install the app again.