The procedures shown on YouTube for changing the fluid for a Corolla CVT range from simply removing the drain plug  and then the nylon tube and then putting back the same amount of fresh fluid as was drained out when the drain plug and nylon tube were removed to dropping the oil pan and replacing the filter and then again putting back the same amount of fresh fluid as was drained out. Obviously the first procedure is much easier, but it replaces less than a quarter of the fluid in the transmission and the dirty filter remains in the transmission. Would it be beneficial to just do the simpler procedure every 30 or 40 thousand miles or so? If not, I'd be inclined to let the dealer do the more elaborate procedure, but then I'd be wondering if the work was really done. My Corolla currently has 70,000 miles and run flawlessly.