I assume you created a custom resource from a dynamic type
1. Delete "Dynamic Types" object
You have to create a resource action with "disposing" action selected. Then execute the action on all "Dynamic Types" object to remove reference from VRA.
2. Remove all references to the custom object. Select the custom resource and in "Where used" tab there should not be any reference to the custom resource in "Service Blueprints" or "Resource Actions"
Then you should be able to delete the custom resource.