How would i simplify this?

What you're looking for is a for loop. The correct format of for loops looks like this:

for variable = startNumber, endNumber, increment do

end

What this does is variable will start at startNumber, end at endNumber, with increment being added to variable each time the loop iterates.

The default value of increment is 1, so if you're just adding 1 each time you can leave it out.

for index = 1, 10, 0.5 do
	print(index)
end

Play around with these numbers and check your output.

To change the position we just need to make startNumber 500, endNumber -500, and increment -1 so that one is subtracted each time.

for i = 500, -500, -1 do
	workspace.fly1.MEOW.Position = Vector3.new(i, 20, 40)
	wait(1)
end