Set up backup DNS as a part of emergency or resilience plans and activate as primary when needed.
Don`t lose your configuration in case of primary DNS problems. Have all of your zones and records stored in backup DNS.
Have a backup of DNS service so you can distribute traffic based on configurations and have redundant DNS service.
Do not rely on just one DNS server, because it’s a single point of failure. If the primary server fails users can not access the desired services. Using a backup DNS server you will have redundancy and your users will less likely experience a disruption of service.