This is one of the few things in this airplane that can kill you so your priority is to immediately remove the threat: disarm the ground spoilers, ensure the throttles do not come to idle, and pull the circuit breakers. Now the threat is gone and you can land.
But there is more to it than that. What follows is from the G450 Aircraft Flight Manual with a few techniques and explanations of my own shown in blue.
This is the only amber WOW fault CAS message, but it is a serious one.
You may or may not get the CAS message but you will not be able to raise the landing gear handle.
Both main gear WOW are in the ground mode while the combined WOW has figured out that the airplane is higher than 147.5 feet. (See G450 WOW for more about this.)
[G450 AFM 3-18-90]
WARNING: DO NOT RETARD POWER LEVERS TO IDLE IN FLIGHT. GROUND SPOILERS MAY DEPLOY.
Your first indication will probably be that the gear handle did not come up and you may fixate on the gear handle and forget the ground spoilers. If you then level off and the autothrottles retard the throttles, the ground spoilers could hurt you.
NOTE: If Rad Alt is failed, WOW indications will display as invalid (cross-hatched) on Flight Controls synoptic / system pages.
LEFT WOW: POP, C-1
RIGHT WOW: CPOP, C-1
What if the airport you just left is 500 RVR and you need to fly an hour away to get back on the pavement? Following the book procedure the gear will not come up and the airplane will not pressurize. Now what? The book doesn't say this but if you really needed to do this to stay safe, pulling the Combined WOW — POP, C-2 — gets all of the airplane back into the air mode, including the landing gear and pressurization. Note: this is a valid G-IV procedure but has been left out of the G-V series for some reason. If I just left KEGE and the weather or my weight precluded an emergency return, I would use this technique to allow me to hop over the mountains and get to Denver. But that's just me.
NOTE: Once below 50 knots, WOW will shift to the GROUND mode
This isn't true. As soon as your wheels spin up you will have normal thrust reverser control and wheel brakes. If you forget to reset the circuit breakers, your thrust reversers will be stuck where you left them below 50 knots and you will lose wheel brakes below 8 knots. Therefore, after you touchdown and before you start to come off the reversers, you need to reset those breakers.