Take it out and put it to the side where he can see it and get used to it that way. Wait a few days and then try it in the cage again or attach it to the outside of the cage for a while and then put it inside.
My Goffin's would not go near the main perch in her new cage. Purchased a custom perch and she wouldn't go near that for many years. She would perch on a smaller perch or hang onto the cage bars. I did everything I could to get her to use the main perch....put treats on it, wrapped toys and bird safe rope around it, etc. Nothing worked. One day she just decided it wasn't scary any more but it took a few years for her to get to that point. Hopefully it won't take that long for your Bourke to accept the new perch.