How to make this show once?

How to make this gui show on enter only? BTW this is the Exit gui but add to it

Gui = script.Parent.Parent

while true do 
wait(49)
script.Parent:TweenPosition(UDim2.new(-2,0,-5,0), "In", "Back", 1,true)
end

Try this, I dont know if it will work

Gui = script.Parent.Parent 
while true do
wait(49)
script.Parent:TweenPosition(UDim2.new(-2,0,-5,0), "In", "Back", 1,true)
script.Parent.Parent:Destroy()
end

Or this

Gui = script.Parent.Parent 
while true do
wait(49)
script.Parent:TweenPosition(UDim2.new(-2,0,-5,0), "In", "Back", 1,true)
end

script.Parent.Parent:Destroy()

Or this

Gui = script.Parent.Parent 
while true do
wait(49)
script.Parent:TweenPosition(UDim2.new(-2,0,-5,0), "In", "Back", 1,true)
end

Gui:Destroy()