Are you talking about a real situation, or are you looking for information on how to act in such a case?
If it actually happened, then usually helping the parrot depends on how tightly the boa has coiled around it and whether the bird is still conscious. The main thing is not to panic and not make sudden movements, because a frightened boa can squeeze its prey even harder. You need to carefully unwind the snake's coils, starting from the tail, slowly and cautiously so as not to damage either the parrot or the snake itself. If the boa has coiled very tightly, you may need help from a second person.
After freeing the parrot, it will need attention - you need to check if it has any injuries, fractures, or breathing difficulties. A frightened bird can be aggressive, so it's better to give it some time to calm down in a quiet place first, and then take it to a vet. The boa should also be left alone after such a scare - snakes often don't eat for a while after a failed hunt.
If you have both birds and a snake in one space, it's best to separate them going forward to avoid such situations.