1) You can register Dynamic DNS service. like no-ip.org.
Step2: Type your information, You can look at the picture
Step 3: Please login your email, you will see "Activate Your No-IP Account" and click Activate Account
3) Once registered, you'll need to download their Dynamic DNS client, use your default logins defined at the registration process. You can download at https://www.noip.com/download
4) Once installed and configured:
Now you can try the hostname directly in your remote desktop application to make sure it is working properly before triggering the domain.
5) Once you have the confirmation, your Dynamic DNS is working properly you can hit the connect button of your VPN.