You don't. You fill it to the right level. If it leaks you fix the leak. Nissan is totally paranoid about overfilling CVT's, and rightly so. Underfilling isn't destructive until it overheats the fluid, but even a small amount of overfill will cause foaming that's very destructive very quickly. It's hard to prove when a CVT fails because of that, so ignorant DIYers could obviously cause a lot of unwarranted warranty repairs. Thus, they made it difficult on purpose. I don't blame them, and if you want to DIY, a bottom-up hand pump and four jackstands aren't much of an investment. Then you can do it right.