The most important stuff has already been mentioned above. If you don't have the manual, you can download it from this side.
If the doorlock tips indeed fell in, you will need to loosen the plastic doorcover. This is glued to the door with a very sticky adhesive. So I would advice to only pry it loose in one corner and see if you can find the tip down in the door.
One more thing, when I fitted my the lock tips again, I found that my remote control did not always seem to work. I traced this back to a sticky doortip that prevent the doorlock from operating correctly because of the friction. So I put a little lube around the bottom of the tip and now it works fine. Also, the tip screws on and has to be inserted from the bottom through the doorpanel. Make sure it works ok before putting back the inner door panel.