Yes, I know how to do this. Been there, done that.
Unless you are very good with jewelers screw drivers, and modifying them, it is best to have a professional do this. The CL mechanism can be damaged if you use too much force in adjusting the screws, and they are often epoxied down to hold position.
If the camera has not been serviced in a while, it is well worth paying the $120 or so to have it CLA'd, meter contacts cleaned, lubed, and RF adjusted.
With that stated; the adjustment screws are under the small plastic cap on the top plate. It is quite hard to get off. You can use some sticky tape to "pull it up a little" then get a small flat blade screwdriver onto the side to pop it up. You will see a wierd looking screw that is realy two concentric screws; a very small fine one on the interior and a split screw exterior to it. They are usually epoxied by the last guy who adjusted it just BECAUSE IT IS A PAIN! Each screw adjusts vertical and horizontal. Yup, you get one in place just to have the other move it off. By the time you converge to a solution, hope that you do not strip the screws or damage the mechanism. If you do, it will cost a lot more to repair than the $120 that Essex in New Jersey charges for a Leica CL standard service! I have no problem adjusting Canons and Nikons. I have popped the faceplate off of my Black Nikon SP to adjust the RF and have removed the focus helical of a Nikon S2 to adjust the film-to-flange distance. I sent the CL to Essex for a service, and was glad I did.