Can anyone suggest how i get booked tickets to a concert in preservation hall in November 2019 from Australia Thank you Cheers Bev

You can purchase tickets online. http://preservationhall.com/hall/

How can I change a reservation?

Check the website when the time is nearer. You can buy front row seats there. Otherwise, just show up an hour and a bit before the show and stand in line. It'll be standing room only, but the room is only about 5 meters long. There's not a bad spot in the house.