Why is this change pitch to 1 script not working?

I have sounds playing with 0 pitch in the PlayerGUI so this script below which is in a GUI button, when pressed it should be changing the Pitch of the sound to 1, but for some reason it's not working.

local plr = script.Parent.Parent.Parent.Parent

function onClick(mouse)
player.PlayerGui.Music.Pitch = 1
end

script.Parent.MouseButton1Click:connect(onClick)

In the output I'm getting:

22:29:31.728 - Players.Player1.PlayerGui.ScreenGui.TextButton.script:4: attempt to index global 'player' (a nil value)

22:29:31.732 - Stack Begin

22:29:31.733 - Script 'Players.Player1.PlayerGui.ScreenGui.TextButton.script', Line 4

22:29:31.734 - Stack End

local plr = script.Parent.Parent.Parent.Parent

function onClick(mouse)
plr.PlayerGui.Music.Pitch = 1 --plr is a variable for I'm guessing the player. Also, is music a Gui or sound?
end

script.Parent.MouseButton1Click:connect(onClick)

If it's a local script you can do Local Player

local plr = game.Players.LocalPlayer --Notice how the LocalPlayer is in the players. Local player is better than writing a bunch of "Parents."

function onClick(mouse)
plr.PlayerGui.Music.Pitch = 1 --plr is a variable for I'm guessing the player.
end

script.Parent.MouseButton1Click:connect(onClick)

Also, there is a shortcut to making scripts with functions in them that are connected to events.

local plr = game.Players.LocalPlayer

script.Parent.MouseButton1Click:connect(function (mouse) --Make it look something like this. Notice how I compleatly got rid of the "onClick" because it's useless now.
plr.PlayerGui.Music.Pitch = 1 --plr is a variable for I'm guessing the player.
end)