can't make the transparency looping?

here's how you would do that. I explain each step in the code:

part = script.Parent --location of your part in the workspace

while true do --this while true do loop makes the code inside the loop run indefinitely 
	

	--this loop starts at zero and goes up to one. every time the loop runs, 0.1 is being added to the variable i and we are changing part's transparency to i. The increments would go as following: (0, 0.1, 0.2 (...) 0.9 1 

	for i = 0, 1, .1 do
		part.Transparency = i
		wait(.1)
	end --end of the first for loop
	
	--This does the same as the other loop but instead of counting from 0 to 1 it counts down from 1 to zero. 
	for i = 1, 0, -.1 do
		part.Transparency = i
		wait(.1)
	end --end of the second for loop


end --end of the while loop

without all the comments it looks like this:

part = script.Parent

while true do
	for i = 0, 1, .1 do
		part.Transparency = i
		wait(.1)
	end
	
	
	for i = 1, 0, -.1 do
		part.Transparency = i
		wait(.1)
	end
end

you initially had it so you added 0.1 every .1 seconds, checked if it was 1, started subtracting. your issue was that once you subtract one, and then you're constantly adding one then subtracting one. if you wanted to do it your way, then you could've done this:

part = script.Parent
i = 0
incrementValue = -1

while wait(0.1) do
	--condition for when i is 1 or more
	if part.Transparency >= 1 then
		incrementValue = -0.1  --make i -0.1 so we're subtracting instead of adding
	end
	
	--condition for when i is less than or equal to zero
	if part.Transparency <= 0 then
	  	incrementValue = 0.1 --make i 0.1 so we're adding .1 instead of subtracting 
	end

	--update i and part make part transparency i
	i = i + incrementValue
	part.Transparency = i
end