For conventional rice cookers (those without the overly complicated computer chip) there are 2 types, the cook-warm type and the cook-off type. Eggs can be cooked in both of them. Just put water in the inner pan and the steamer insert in the first type and press the button. There should be a water level indicator to follow on the inner pan, the steamer insert or in the booklet that came with the rice cooker. For the second type, water is also put in the inner pan and eggs into an ad hoc steamer that goes inside or if there is an above steamer, the eggs are actually steamed but it does take longer.

The accessory divot tray for eggs is so much easier as it holds the eggs in the correct position. Sadly, my rice cooker is ancient and they don't sell accessories for it any more