Set a Static IP on VM within Virtual Network connected to a Local Network

I have a Virtual Network connected to a Local Network, I have just created a new VM that I want to use as my DC and Primary DNS. the server is currently set by DHCP of 10.100.3.4 and I want to set it as 10.100.3.203 I have set the Virtual DNS serves as 10.100.3.203.

I RDP into the VM and changed the adapter from automatic to 10.100.3.203 and then was unable to connect to the server anymore.

I changed the VM size and am able to get back into the actual server via RDP.

I will be adding 30 to 40 more servers and would like to assign static IP's to all of them.