How do you replace the rear brake light on the rear door of a 1999 Toyota Sienna?

I called a Toyota dealer with this same question. You have to remove the inside panel. Mine was on the driver side, so I slid off the cover to the hand strap and unscrewed it. Then I pried back the panel, just on the side I needed to access. It just pops off, but do it carefully, so you don't break the little plastic parts that pop in.

From there you can access the back of the light. Twist the bulb holder until it will pull out. Replace the bulb and put everything back together.