How to Position Region3 in front of the player?

I just started learning about region 3, and I want to make a region that appears in front of the player when he presses a key. The problem is that the region3 always get in the same direction no matter how I move the player. can someone help me settle it please??

Here is the script,

local c = plr.Character
	
	local Reg = Region3.new(c.HumanoidRootPart.Position-Vector3.new(0,2.5,2.5),c.HumanoidRootPart.Position  +Vector3.new(20,2.5,2.5))

	local Part = Instance.new("Part",workspace)
	Part.CFrame = Reg.CFrame
	Part.Size = Reg.Size
	Part.Anchored = true
	Part.CanCollide = false
	Part.Transparency = 0.8
	
	local Rtable = workspace:FindPartsInRegion3(Reg,c)
	
	
	for i,v in pairs(Rtable) do
		print(v)
		if v.Parent:findFirstChild('Humanoid') and v.Parent.ClassName == 'Model' and v.Parent:findFirstChild('AoEDebounce')== nil then
			local Deb = Instance.new('BoolValue',v.Parent)
			local BV = Instance.new("BodyVelocity",v)
			BV.MaxForce = Vector3.new(25000,25000,25000)
			BV.Velocity = c.HumanoidRootPart.CFrame.LookVector * 50
			game.Debris:AddItem(BV,0.5)
			Deb.Name = 'AoEDebounce'
			game.Debris:AddItem(Deb,1)
			v.Parent.Humanoid:TakeDamage(30)
		end
	end

This is because you gave constant vectors (vectors that always stay the same) to specify a direction in your Region3 arguments. You must base it off vectors that will be based off the player's direction, namely the unit vectors which you have used one (CFrame.LookVector).

By using CFrame, it will be as simple as changing your Reg variable to this although I will add a CFrame variable and number variable to make the Reg variable simpler and shorter to read:

local cf = c.HumanoidRootPart.CFrame
local Z_multiplier = c.HumanoidRootPart.Size.Z/2 -- becomes negative later because -Z is forward, by multiplying position Z by this, you will reach the front surface of the object
local Reg = Region3.new(cf * CFrame.new(0,2.5, -(Z_multiplier + 2.5) ), cf * CFrame.new(20,2.5, Z_multiplier + -(Z_multiplier + 2.5) ))

You might need to adjust the CFrame coordinates for X or Y if the result is still undesirable.

If only it was about CFrame, but, in region3 you can only use Position / Vector3 :( . I tried your idea but it still doesn't work. It say: invalid argument #1 to 'new' (Vector3 expected, got CFrame)

Try using @ArtFoundation's answer and use CFrame.Position wherever you are currently using CFrame.