I not 100% sure how CVT's are serviced or what possible to do. But at 40k, the fluid shouldn't be too worn out. I would think a minimal service is sufficient.

I ask for drain and refill. If they refused, find another shop. The reason behind that is you do not need to flush the transmission and you don't benefit from doing it either. Also, you will be charged more compared to drain and refill. 

See below for what is involved by Toyota Master Mechanic The Car Care Nut:  He recommends to change every 60,000 miles (drain and fill).  Scotty is recommending every 30,000 miles.  With CVTs, I would follow Scotty’s for piece of mind.  Ideally, it would be better to have an independent, honest mechanic that works on Japanese vehicles (esp. Toyota’s) do it for you if you don’t do it yourself.  Also, be sure to use the correct transmission fluid (and he outlines it in the video).  CVTs are not Toyota’s strongest/best transmissions so I would go every 30,000 miles to be safe, and use only OEM fluid.

https://m.youtube.com/watch?v=eRxSu4-4ojo

Hello yes i have A 2018 Toyota Corolla le with a cvt transmission i was Wondering is it ok to have the dealership flush my transmission i only have 40k miles had never have had the fluid changed