Windows: Migrate from Conditional Forwarder to be Secondary DNS Server

Wanted not to affect the DNS usable in another office, such as DNS Servers in one Office required patching. 

Migrating the setting from Conditional Forwarder to be Secondary DNS Server.

What's secondary DNS Server, https://www.cloudflare.com/learning/dns/glossary/primary-secondary-dns/

... secondary DNS servers contain zone file copies that are read-only, meaning they cannot be modified. Instead of getting their information from local files, they receive pertinent information from a primary server in a communication process known as a zone transfer.

When to be a Secondary DNS Server, requires to remove the Conditional Forwarding first. If not:

DNS

The zone cannot be created.

A conditional forwarding zone already exists for that name.

DNS

Warning: This is an Active Directory-Integrated forwarder. If you decide to delete this forwarder from the DNS server, it also will be deleted from Active Directory. The forwarder also will be deleted from all DNS servers that load this forwarder from Active Directory.

Click Yes if you want to remove the forwarder from both Active Directory and the DNS server.

Click No if you don't want to remove the forwarder.

Update