From mmirecki:

Out of the box, when a host is installed, it uses the "ovirtmgmt" network to set up OVN tunnels (connecting the OVN hosts).
But, the user might want to use another network for this purpose.
This can be done in mutliple ways:

1. Centrally from engine, using ansible:

cd /use/share/ovirt-engine/playbooks

Create a new playbook (for example change-ovn-tunnelling-network.yml):
"""
- name: Change OVN tunneling network
  hosts: ovirt_cluster_<cluster name>

###
for example:
  hosts: ovirt_cluster_test-cluster
###

  vars:
    ovn_central: <IP of ovn central on the network>
    ovn_tunneling_interface: <name of ovirt network to be used for tunneling>

  roles:
    - ovirt-provider-ovn-driver
"""

Run the playbook:

ansible-playbook --private-key=/etc/pki/ovirt-engine/keys/engine_id_rsa -i /usr/share/ovirt-engine-metrics/bin/ovirt-engine-hosts-ansible-inventory  change-ovn-tunnelling-network.yml

2. On each host separately:
Run the following vdsm-tool command:

vdsm-tool ovn-config <ovn central ip> <tunneling ip or network name>