Why it prints but can't make the Part CanCollide to false?

The problem is, that you have two if. So firstly, it check if a=1, and if it is, it sets to cancollide false and transparency 0.7. But the problem is that it sets to a=0, and stops the first if. Then comes the second if, and the a currently is 0, because it was setted to 0 at the first if. And runs the second if, then sets back to cancollide true and transparency 0 So you just need one if, and then a elseif, not two if. Here, try this:

local s = script.Parent -- the Parent is a Part that has ClickDetector as a Child.

script.Parent.ClickDetector.MaxActivationDistance = 8
 
local a = 1
 
script.Parent.ClickDetector.MouseClick:Connect(function ()
 
    print("clicked")
 
    if a == 1 then  -- I wanted this to be worked when first clicked,but never worked.
 
            a = 0
 
        s.Transparency = 0.7
 
        s.CanCollide = false
 
    elseif a == 0 then
 
        a = 1
 
        s.Transparency = 0
 
        s.CanCollide = true
 end
 
end)