Loknath, interestingly enough, it is not in the manual. Try this information from the lexusownerclub.com. Remove the base cover (spread the two sides then lift it up). There is a plastic tab that prevents the wiper to be lifted up, because it's blocking the shaft on its way up. This tab is part of the base cover. It's inside the cover. You van cut it off with the base cover removed. After that, you can remove the blade just like the front ones.The missing tab will not impede the function of the wiper blade.

There are some more directions, essentially the same, on here. Also, check with your dealer, there was a TSB about improving the wiper arm assembly. The reference for that is TSIB # BO008-04, of course it depends on the year of your Lexus, but it should still be covered. Hope this helps, good luck.