How do I make a script to change some values in a part?

few things wrong with your code your code:

function onTouched(part) -- no bad

CrackSound.SoundId = "rbxassetid://131144461" -- what is cracksound????
this.Touched:Connect(function(part) -- do hit instead
        if part.Parent:FindFirstChild("Humanoid") and true then -

        end
        BrickSound:Play()
    transparency = 1
    CanCollide = false
anchored = false
end

edited code:

local part = script.Parent
local CrackSound = Instance.new("Sound", part)
CrackSound.SoundId = "rbxassetid://131144461"
part.Touched:Connect(
    function(hit)
        if hit.Parent:FindFirstChild("Humanoid") and true then
            CrackSound:Play()
            part.Transparency = 1
            part.CanCollide = false
            part.Anchored = false
        end
    end
)

Explanation:

You did a few things wrong. function onTouched(part) is not needed as you did this.Touched:Connect(function(part)

CrackSound.SoundId I believe you forgot to reference that in the code, so I did script.Parent.

BrickSound isn't CrackSound?

transparency = 1
CanCollide = false
anchored = false

Remember, Roblox is case sensitive and these are children/properties of the part.

So first of all, you haven't defined the sound variable. Secondly you do not the and true part, as it is unnecessary and just causes your script break (potentially.) Thirdly, you need to define the variables if you want to access the properties. Roblox introduced variables to make your life easier.

local part = script.Parent
local crackSound = script.Parent.CrackSound
crackSound.SoundId = "rbxassetid://131144461"
function onTouched(hit) --Use a different parameter name in order to not confuse yourself.
    if hit.Parent:FindFirstChild("Humanoid") then --You do not need the 'and true' part. Unless if you're using a debounce.
        crackSound:Play()
        part.Transparency = 1
        part.CanCollide = false
        part.Anchored = false
    end
end

script.Parent:Connect(onTouched) --Make sure you connect the function after you defined it.

(Note: I seen that you said crackSound is not a valid member of part . That means you haven't put the CrackSound Sound as the child of the Part. Placement is key, and if you place it incorrectly, it may break your script, having an error, or not.)