Open the vDC of organization. Go to the vApp tab. Select the necessary vApp (for example, vApp_Administrator_1) and open it.
In vApp_Administrator_1 go to the Networking tab. Add the network to vApp by clicking NEW.
Choose Organization VDC network, as it was already created during the preparation of vDC.
Select the right network.
Click Add and after closing the dialog window, click Apply in the bottom right corner.
The network will then be displayed in vApp and you can connect the machine to it. This is done by adding a network adapter when the VM is off.
Adding the network adapter to the virtual machine: