The Q-Cal Booking app on your meeting room displays can be updated directly from app.q-cal.net.
Go to Views > Meeting Room Displays.
Here you'll see all the screens on your account, along with their Version and Activity.
The circular icon on the far right (Activity column) shows whether a screen is currently online. A screen that's offline can't be updated remotely — check that the screen is powered on and connected before trying again.
If a newer version is available for an online screen, a small update icon appears in the Version column. Click it, then choose whether to update just that screen or all screens with an update available.
A few seconds after starting the update, a pop-up will appear on the display itself, asking whether it's okay to update Q-Cal. This has to be manually confirmed on each screen that's being updated.
If a screen's version is too old to update this way, you can update it manually using a USB stick:
If the screen doesn't prompt you automatically, open the device's file manager, select the USB stick, and tap the install file (the APK you copied over) to start the update manually.
Note: you may need to manually reactivate the update prompt after accepting any security warnings your device shows, as Android's own security flow can interrupt the process partway through.