Hi,
The most common and recommend way to specify a DC for authentication is by creating site for the servers and DC, put them into the same site.Then the servers will already contact this DC for authentication firstly .The servers or clients will contact other DCs only if this DC in the same site is unavailable.
Or you can considered specifies the weight (or weighted priority) of this domain controller.(HKLM\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters) The weight determines the probability that a client contacts the domain controller when it selects from among domain controllers with the same priority. Domain controllers with the highest weight are most likely to be contacted.
For more details about how to set the value, you can refer to :
https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-2000-server/cc957291(v=technet.10)?redirectedfrom=MSDN
Note:Do the back up before any changes for the registry.
There are some commands to specify the DC, but were temporary .Once the servers were reboot , they will contact a DC randomly.
nltest /Server:ClientComputerName /SC_RESET:DomainName\DomainControllerName
klist add_bind CONTOSO KDC.CONTOSO.COM
Best Regards,