Hello
It appears you have changed the internal private IP of the VM instance and not able to access now. However, you can access the Windows instance directly using the serial port console. Here is the
documentation link for enabling and connecting through serial console port on GCE VM instances. Note that, Windows instance interact through serial port 2.
After login, it will bring to the Windows command prompt from where you can run commands to make the required changes.
You can run following example commands to set IP address and DNS dynamically for the Windows VM instance interface name "Ethernet" on GCE.
netsh interface ip set address "Ethernet" dhcp
netsh interface ip set dns "Ethernet" dhcp
Once set, verify the RDP connection to the Windows server VM.
I hope it helps.