I haven't changed mine, but there are plenty of Youtube videos detailing the replacement from the likes of deutche autoparts.
On my previous mk7 GTi PP, I had them changed at a VW main dealer as I started to get warning lights.
I am intrigued, are you able to keep on top of this by actively topping up the coolant level?
Obviously it won't fix itself, unfprtunately.
What is the mileage on your CS when this started to happen, just so I can prepare myself.