How do I change just one axis in a CFrame?

So I wanna make a turret that moves to face a players mouse so I did:

wait(5)

local Plr = game.Players.LocalPlayer
local Mouse = Plr:GetMouse()
local Tank = game.Workspace:FindFirstChild(""..Plr.Name.."'s_Tank")
local mousePosition = script.Parent.GetMousePosition.MousePosition
local FakeTurret = Tank.FakeTurretHitbox

while wait() do
	FakeTurret.CFrame = CFrame.new(FakeTurret.CFrame.p, mousePosition.Value.p)
end

This worked but I only wanted the turret to move to the target on it's y axis, so I did this:

wait(5)

local Plr = game.Players.LocalPlayer
local Mouse = Plr:GetMouse()
local Tank = game.Workspace:FindFirstChild(""..Plr.Name.."'s_Tank")
local mousePosition = script.Parent.GetMousePosition.MousePosition
local FakeTurret = Tank.FakeTurretHitbox

while wait() do
	local cframe = CFrame.new(FakeTurret.CFrame.p, mousePosition.Value.p)
	cframe.x = 0
	cframe.z = 0
	FakeTurret.CFrame = cframe
end

This didn't work though, the output said "18:43:42.868 - x cannot be assigned to 18:43:42.869 - Script 'Players.Player.PlayerGui.TurretMover', Line 13 18:43:42.870 - Stack End" I went to the wiki and found out .x .y and .z are read only. So if I can't change the axis like that how else could I?