You can delete specific nodes from an overcloud with command:
openstack overcloud node delete --stack $STACK_NAME --templates [templates dir] <list of nova instance IDs>
This command updates the heat stack with updated numbers and list of resource IDs (which represent nodes) to be deleted.
If you passed any extra environment files when you created the overcloud (for instance, in order to configure network isolation), you must pass them again here using the -e or --environment-file option to avoid making undesired changes to the overcloud.
A list of nova instance IDs can be listed with command: