Boot up off CentOS7 and at the below menu press escape:
Once you have pressed escape you will be presented with the following command line:
At the boot: prompt type in the following line and change 'YourToken' with your giving token.
This assumes that the VM is attached to a DHCP network and that the gateway and DNS servers are automatically provided.
If the network is not DHCP enabled then the following line must be entered and replace the relevant values with your network settings.
Press Enter to proceed with the install.