when using my crockpot multi cooker, di i let it go to keep warmm for natural venting or do i press stop

You need to follow the recipe instructions, which will tell you if you should let it release naturally as it cools, or vent it to quickly release pressure. Some things, like hard boiled eggs, will call for a quick release. Others, like for a pot roast, will say to let it release naturally. If you are going to do a quick release, then turn off the keep warm function. Otherwise, you can leave it go.