The Operations Manager's firewall uses the concept of Firewall Zones (such as LAN & WAN) to define which Permitted Services (such as ssh & https) are available on its Physical Interfaces (such as NET1 and Cellular Interface). When a Service is added to a Zone, all requests to access the Service arriving in the Zone are permitted.
Alternatively, you may use Custom Rules to only permit access to requests arriving from a matching source network address. Custom Rules utilize the firewalld Rich Rule syntax, allowing fine-grained control and advanced applications.
For step by step instructions on using Custom Rules to restrict access to HTTPS from a trusted source network only, refer to Example 2 in this article.