Glad to help: First, you need to get the OVR Toolkit from the Steam store, then you launch SteamVR and the Toolkit via the Steam app. In MSFS, the Toolkit menu will appear “linked” to your left controller. If not, you need to double-click the inside-buttons (middle fingers) on both controllers simultaneously to activate the Toolkit.
With its menu, you can create new windows to contain either whole desktops or individual apps.
Cheers