This is not an Ignition problem to solve. The vast majority of the work involved in making an Ignition gateway accessible over the public internet is general IT knowledge that's not specific to Ignition. I'll also add that if you do not know what you're doing, it is incredibly dangerous to expose internal servers to the public internet. For any period of time.
I would consider it an absolute requirement to have a public domain name, a valid SSL certificate, and HTTPS enabled before even considering exposing an Ignition gateway to the world. A safer option would be to set up a VPN, but even knowing what your options are in this space is basically just fundamental IT knowledge.