GTM as DNS Conditional Forwarder for Same Domain Name

dear Experts,

I need guidance to implement the GTM Module. I have a domain that has been hosted on two different data centres. In each data center I have two F5 devices. Each data center has two DNS servers that hosts the example.com. At the moment, DNS requests were answered by DNS on the local servers of each data center. But if the Internet link to one of the data centres is disconnected, the hosts hosted in that data centre will be unavailable.

I want to configure the GTM Module to have the Conditional forwarder. In such a way that monitors the servers of each of the data centres, if the server is available, provide the user with an active DNS address for the DNS server.

would you please provide a solution for this case