How Can I Change the CanvasPosition with a TextButton?

[PLEASE MARK THIS ANSWER AS ACCEPTED IF IT WORKS]

To tween canvas position, you do not use :TweenPosition(), instead you tween it like you would with any other Vector2 property.

script.Parent.MouseButton1Click:Connect(function()
    local TweenService = game:GetService("TweenService")

    local scrollingframe = script.Parent.Store.ScrollingFrame

    local goal = {}
    goal.CanvasPosition = Vector2.new(0, 0)

    local tweenInfo = TweenInfo.new(0.5, Enum.EasingStyle.Linear, Enum.EasingDirection.InOut)

    local tween = TweenService:Create(scrollingframe, tweenInfo, goal)

    tween:Play()
end)

You don't use UDim for CanvasPosition or TweenPosition. To achieve the same result you will want to use TweenService.

For example, to move the canvas down you would do this:

local tweenService = game:GetService("TweenService")
local canvas = script.Parent.Store.ScrollingFrame

script.Parent.MouseButton1Click:Connect(function()
    tweenService:Create(
        canvas,
        TweenInfo.new(0.2),
        {CanvasPosition = canvas.CanvasPosition + Vector2.new(0, 20)}
    ):Play()
end)