1. Use DFS namespaces to abstract the folder share name that the clients will use to access the share.

https://docs.microsoft.com/en-us/windows-server/storage/dfs-namespaces/add-namespace-servers-to-a-domain-based-dfs-namespace

1. Setup DFS replication when adding the two folder targets in the DFS console. I believe it asks if you want to set it up when you add the folder targets.

https://docs.microsoft.com/en-us/windows-server/storage/dfs-namespaces/add-folder-targets

1. Disable referrals to the secondary share, enable it and disable the primary if the primary goes down

https://docs.microsoft.com/en-us/windows-server/storage/dfs-namespaces/enable-or-disable-referrals-and-client-failback

1. Get a proper backup strategy implemented. Your secondary server helps you achieve high availability, it is not a backup.