Dried bird's nest is not cooked so much as coaxed. It is a protein that has been dehydrated, and the job is to put the water back without wrecking the structure. Two steps, one rule.
Step one: soak
Put the nest in a bowl of cold water — not warm, not hot — and leave it until the strands have gone soft and separated. For instant or pre-cleaned nest this can be as little as 30 minutes to an hour. For whole dried nest, allow three to four hours, or leave it overnight in the fridge.
It should roughly double in volume. Once soft, go over it with tweezers under good light and lift out any remaining down. Even carefully cleaned nest usually has a feather or two.
Drain and rinse. Do not soak in hot water to speed this up — you will start dissolving the nest into the water you are about to throw away.
Step two: double-boil
Put the drained nest in a lidded ceramic or glass jar with just enough water to cover it. Stand the jar in a pot, add water to the pot until it comes partway up the sides of the jar, and bring the pot to a boil.
Then turn it down. The water around the jar should sit at a gentle simmer, not a rolling boil, for 30 to 45 minutes. Whole dried nest may want an hour.
This is the method called chưng cách thuỷ, and the reason for it is simple: the nest never touches direct heat. The steam does the work, the temperature stays moderate, and the strands soften without breaking down.
The one rule
Do not boil it directly. Bird's nest put straight into rapidly boiling water loses its texture and much of the point. Every traditional method is a variation on gentle indirect heat, and every one of them exists for that reason.
Sweetening and serving
Add rock sugar, pandan, red dates or goji in the last five to ten minutes, not at the start. Sugar added early draws water out of the strands and firms them up.
Traditionally it is eaten warm on an empty stomach, in the morning or before bed. A serving is small — three to five grams of dried nest is a normal portion, which is why a 250g package lasts a long time.
If you would rather not
All of this takes an evening of attention, which is exactly why instant and ready-to-drink formats exist. They are prepared the same way at scale. If the ritual is not the point for you, the bird's nest collection has both — dried nest for people who want to do it properly, and prepared jars and bottles for people who want the food without the evening.