See, I knew John would get it sussed
So, if you're going to do it yourself then as John says, you'll need Techstream and a Windows laptop to install it on. The good thing is that you don't have to bother about an OBD2 code reader now because Techstream does so much more.
In order to connect the laptop to the car you'll need a miniVCI cable, a selection of which can be found here on eBay These cables almost invariably come with a pirated copy of Techstream, which is the actual diagnostic software Lexus techs use in the dealer workshops. Of course, I can't condone the use of pirated software, that's a matter for your own conscience. The proper way would be to freely and legitimately download it from here and then pay for a block of time to use it.
Whichever way you decide on, you'll need that miniVCI cable to connect the laptop to the car anyway.