How to delete custom resource and remove item from items tab?

I am trying to remove the custom resource which I defined earlier but it is not allowing and giving me the error below.

"Cannot delete a custom resource that is in use. Referenced in: Resource"

For that I tried to remove an entry from the "Items" tab which would have any association, but there too I do not have any option to remove. I had provisioned a resource from the service blueprint and created a resource action "Delete a volume" without the selection of "Disposal" and hence the entry in "Items" tab still remains. How do I cleanup this now?

Thanks & Regards

Sandeep Zende