If the pet has a collar always check if it has a nametag. Usually owners will pop contact details on there.
Firstly try to contact the owner, failing this we recommend you take the lost pet to a local vet or animal shelter (if you cannot do this please contact an animal warden) one of those professionals will be able to scan the pet to see if it has a microchip and reunite the lost pet with the rightful owners.
If not, please take the lost pet straight to a local vet or contact your local animal warden. This will be the quickest and easiest way to find the owner. They will be able to scan the pet for a microchip number and contact the owners of the pet.
The Environment Protection Act 1990 states any finder of a stray dog is to return the dog to its rightful owner, or contact a local authority (dog warden service) to report it and have the dog picked up.