Hi Amit,
A) In Azure portal, please navigate to your domain controller VM -- click Network settings blade, next on right click on the network interface. Once on network interface page, click on the ipconfig on right and set the Private IP address to Static.
B) In Azure portal, please navigate to your Virtual Network -- DNS servers blade. Select Custom, and enter the private IP address of your domain controller.
C) Inside of your domain controller VM, open DNS Manager, on left right-click on the server name -- Properties. On Forwarders tab, add 168.63.129.16 address.
D) Restart the second VM (so that DNS settings change will take effect) and then join it to domain
Please click Accept Answer and upvote if the above was helpful. If something is unclear add a comment below.
Thanks.
-TP