Apple has removed native support for the popular PPTP VPN protocol since macOS 10.13 High Sierra due to security reasons. If you are using more modern versions of macOS, configure the connection using the L2TP, IKEv2 or OpenVPN protocols.
To setup the outgoing IP open the http://setup.securevpnconnect.netwhen VPN-connection is active. Select the IP address you need and click the green check mark. The address is changed instantly, and the next time you connect to the VPN, the previously set address will be used.