How do you change only the position of 1 axis?

I'm having difficulty on this one, I was wanting to change only the y's axis.

Main help part of script:

local part = Instance.new("Part", workspace[plr.Name].Torso)
part.CanCollide = false
part.Anchored = true
part.Size = Vector3.new(1, 1, 1)
part.Position = Vector3.FromAxis(Enum.Axis.Y + 10) -- ?
-- (or)
part.Position = Vector3.FromAxis(Enum.Axis.Y(Enum.Axis.Y + 10)) -- ?

Whole script:

local plr = game.Players.LocalPlayer
wait(2)
local part = Instance.new("Part", workspace[plr.Name].Torso)
part.CanCollide = false
part.Anchored = true
part.Size = Vector3.new(1, 1, 1)
part.Position.Y = part.Position.Y + 5
local mesh = game.ReplicatedStorage.Pet
mesh:Clone().Parent = part
local direction = CFrame.new(part.Position, plr.Character['Left Leg'].Position).lookVector
local increment = direction * 4
while true do
    wait()
    part.CFrame = game.Workspace[plr.Name]['Torso'].CFrame + (direction * increment) + Vector3.new(-5, 0, 0)
    part.Rotation = game.Workspace[plr.Name]['Torso'].Rotation + (direction * increment) + Vector3.new(-1, -2, increment)
end

I would appreciate any help.