Well if your Server has no internet connection because the network settings are wrong, you need to find a way to access your Server without Internet.
Depending on where that server is set up, there are a couple of different ways to do this. One would be to take a monitor and keyboard and walk to the server, plug yourself in and change the network settings. If that is not possible because the server is hosted in a datacenter you don't have access to, you could ask for them to give you a KVM. That way you can have access to a keyboard and monitor attached to the server via the internet.