Do you mean that your users must be able to access your PPM environment from an internet connection? If that's the case, it's a network configuration operation that's required, there's nothing specific to do on your PPM Server.
Of course, you should carefully read the contents of the PPM Security Guide, as exposing your PPM Server to internet traffic also exposes it to potential attackers, and you'd better double check that it is securely configured.
Note that if you are unsure about how to get that properly done, you might consider opting for a SaaS based PPM hosting. HPE or some HPE-certified partners have great PPM SaaS offers and will take care of migrating your current PPM data from on-prem to SaaS.