This part is luckily - very easy!
The only o-rings that need maintenance are the 3 ones located under the end cap.
There are more o-rings in the camera (e.g. around the lens or inside the end cap) - these should not be touched.
The most important to pay attention to, is that the o-rings are always shiny, clean (with no debris, hair or dust on!) and have no scratches or breaks.
If the o-rings look dry, you should put a thin layer of o-ring grease on. You can use your finger, tissue or brush to do so.