ProximityPrompt.Triggered

I need a lil help with this. i dont know what argument to use inside the fireclient

ERROR: Argument 1 missing or nil

local GUI = script.Parent.Hats
local part = script.Parent

part.ProximityPrompt.Triggered:Connect(function(player)
if not player.PlayerGui:FindFirstChild("Hats") then
	local clone = GUI:Clone()
	clone.Parent = player.PlayerGui
else
	game.ReplicatedStorage.ShowGUI:FireClient()    <---- HERE (WHAT ARGUMENT)
end		
end)

One of the arguments should definitely be the player / client you’re firing to!

In this case, :FireClient(player) would fire and therefore affect the player who Triggered the Prompt