You can set the F4 key on the Slim X1 Bluetooth Backlit Keyboard to open Mission Control instead of the App Switcher.

1. Go to System Settings > Mission Control.
2. Select the F4 key next to Mission Control.

Because the F4 key already has a shortcut programmed on it, you will need to hold the FN key while pressing F4 for your new setting to take over. You can also pick a different key from that dropdown if you prefer.

Please note: the F3 and F4 hotkey functions cannot be fully reprogrammed, because the keyboard is built for Apple devices that use Spotlight Search (F3) and the App Switcher (F4).