First ensure the bird has some water available, and give it some seed in case it’s hungry (parrot seed is fine, or even some rice, if nothing else is available try bread, pigeons do not eat meat.)
Check the bird’s legs for a registration ring (lifetime band made of anodized aluminium or plastic). Some breeds have long foot feathering ,so you may have to hunt through this to find it, often in these breeds the ring may be up high on the thigh. Once found write down all the numbers and letters on the ring.
If the letters “ANPA” appear, you are in luck, as the ring was issued by the Australian National Pigeon Association (ANPA) and can be traced to the the club and individual who bought the batch the ring number was in, and thus bred the pigeon.
To search out the owner of an ANPA rung bird yourself, check out the Ring Registry.
Important Note: If the ring does not have the letters ANPA, you will need to check other sources. if the ring has a clear plastic protective coating, it probably is a racing pigeon. So you will need to check for Racing Pigeon clubs on the web, or in the telephone book under clubs and societies.