Loknath, interestingly enough, it is not in the manual. Try this information from the lexusownerclub.
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.