According to Google documentation, you can connect to your server via PSESSION.
First, You need to open port 5986 from your GCP Firewall.
Then Open Powershell on your local computer and type in this command:
Enter-PSSession -ComputerName [EXTERNAL_IP_ADDRESS] -UseSSL
-SessionOption (New-PSSessionOption -SkipCACheck -SkipCNCheck)
-Credential $credentials
If the port is blocked from your windows firewall, then you can try accessing CMD from Serial Console.
Instructions Available here

After you have access to your CMD/Powershell, you can easily turn them off with this command:
netsh advfirewall set allprofiles state off
If all of above fails, you can try doing it through startup script:
Documentation Here
Hope This helps,
Shahriar