You can edit the failover criteria after the FTD HA pair is created.
- In the navigation bar, click Devices & Services .
- Select the active device of the FTD HA pair.
- In the Management pane, click High Availability.
- In the Failover Criteria window click Edit.
- Make any necessary changes and click Save.
- Review and deploy the changes now you made to the active device, or wait and deploy multiple changes at once.