How to make a GUI Button that can change a value?

This will need to be in a script inside of the button. You can modify the script.Parent path as needed if your script is elsewhere.

script.Parent.MouseButton1Click:connect(function()
    game.Workspace.ExampleValue.Value = 1 -- replace with needed path
end)

Scripting Helpers is not a request site

But I can give you some help

local textButton = -- TextButton location here.   Or just script.Parent if the script is inside of the button
textButton.MouseButton1Down:connect(function() -- Connect the function
    --Here you just have the value change, example:
game.Workspace.NumberOfClicks = 19
end

Of course you would add a lot more lines to fit your liking, but you get the point.

script.Parent.MouseButton1Click:connect(function()
    game.Workspace.TheValue.Value = 0 -- Change "0" to what you want the value to equal
end)