Before you do anything: Please notice that birds are very fragile and you can easily break some bones if you do not know how to carefully capture the bird!
If you do not have any experience with birds I highly recommend you see if you can find some help nearby.
If you try to capture the bird yourself, then it is important to stay calm or you will likely scare it off!
Try to speak to the bird in a calm voice and see if it react – does it look scared? Then back away! If the bird does not seem to be scared then keep talking to it in a calm voice – if the parrot is tame it may come closer to you and perhaps even follow you into the house.
If you or any of your neighbors have a pet parrot yourself you can try moving its cage out in the garden – maybe this will get the attention of the wild bird and allow you to capture it. Try if you can use the other pet parrot to lure the escaped parrot into the house.
If the bird continue to stay in your garden you can provide a bowl of water and food and see if it is hungry. It is much easier to capture the bird later if it is comfortable with a specific location. With any luck you may be able to move the bowls closer and closer to the house until you can lure it inside where it will be much easier to capture.
If the bird is just sitting on the ground it may be ill so you need to capture it and get to a veterinarean as soon as possible. Carefully approach the bird from behind – you can have an assistant talk to the bird to attract its attention so it doesn’t notice you slowly getting closer. Use a soft fabric like a pillowcase or bed sheet to carefully catch the bird.