Propagating Alocasia from a bulbil is relatively easy so long as you have access to a source of heat such as a radiator or a heat mat.
Take a bulbil from an adult alocasia
This is an alocasia bulbil on a stolon. Alocasia produce lots of bulbils, most of which will be under the soil but occasionally the stolons will hit the edge of the pot like in this picture. It's best to wait until the bulbil is about 1cm in diameter for the best chances of this method working.
Cut the bulbil off the stolon at the base of the bulbil. At this point you should immediately move on to the next step. If left too long the bulbils form a protective brown sheath which makes it harder to kickstart growth. It's possible to take separated bulbils which are covered in a sheath and have success - use tweezers to gently pull back the sheath exposing the live surface below before the next step.
Plant it and keep it warm and moist
Take the bulbil and place it in some potting soil with the top pointing up and slightly exposed. The top is the pointy side where new growth will form. Putting some damp sphagnum on top of the planted bulbil will keep it moist and improve odds of success.
Place the pot on a source of heat. A heat mat for propagation is best. Otherwise wrap the pot in a plastic bag to top the container drying out and placing it on top of a book on a radiator will work. Do not place the container directly on a radiator without something to block some of the heat - it is too hot and will dry out the soil and kill the bulbil.
Wait for growth
After a few weeks you will notice the bulb putting out leaves and that it has rooted into the container. You can pot it on into a larger container at this point and safely remove it from the heat mat.