Powershell to enable Audit Policy on already deployed content type

Hi,

I have created the custom content type and this content type I am using on the library. Multiple items got created using this content type.

Now I want to enable Auditing on this content type. I did through the UI and observed that this will affect only for the new items which will get created with this content type. Its won't apply auditing on the existing items which already got created with this content type previously.

So I need to do it through power shell for existing item's content type. I tried a lot but no luck.

Can anybody help me out in this?

Thanks