Be certain that it is okay to approach the pet. From your Pawscout app, you will be encouraged to contact the owner of the pet to let them know of their pet's whereabouts.
When the owner is reunited with their Lost Pet, navigate to your map menu, generate the options with the (+) symbol, and choose Found Pet. The pet needs to be "In range" in order to report your pet as found.
If you do not have the Pawscout app and come across a lost pet with the Pawscout tag, download the Pawscout app for iOS or Android and create an account. Once signed in, you will be alerted that you are near the lost pet and asked to contact their owner.