Hi @Arief Hardiansyah ,
You can refer to the steps below:
Map the Internet side (public) IP address and TCP port to the inside (private) IP address and port. This is because your internal network will use private IP addresses that are not directly accessible on the Internet (10.x.x.x or 172.16.x.x or 192.168.x.x addresses). This process is known as network address translation (NAT).
Set your firewall to port forward Port 80 to your internal server running SharePoint.
When you made sure that you can access a web application, then you need to make sure that this IP is mapped to a domain name(using Alternate Access Mappings). Check the detail steps at here.
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