To bathe a pet bird, you can provide a shallow dish or a bird bath designed for them to bathe in. Fill it with lukewarm water that is shallow enough for the bird to stand in but deep enough for them to splash around in. Place the bird bath in the cage or in an area where the bird feels comfortable. Let the bird decide when it wants to bathe, as some birds may prefer to bathe in the morning or evening. Ensure the bird is supervised during bath time and remove the water when they are done to prevent chilling.