I once needed to open remote access via the WAN port to a Huawei HS8346X6-C ONU. I periodically had to open the web interface and forward ports to various devices. However, it turned out that this ONU didn’t have Remote Management in its settings. So I contacted the supplier in China for new firmware.
The file I requested from the supplier:
http://files.ixnfo.com/Firmware/Huawei/HS8346X6-C/HS8346X6-C_V500R022C00SPC436_001_osgi_hisi_unicom_ax_v5_framework_plugin_all_encrypt.zip
After updating the firmware, Remote Management still didn’t appear in the menu, but the Access Control menu now allows you to select the WAN port and Source Address from which connections are allowed. However, after some time, the access rule would somehow become disabled, and remote access would disappear. After re-enabling it, the problem would reoccur later. Unfortunately, there wasn’t a newer firmware update available yet.
See also my article:
How to configure ONT Huawei HS8346X6-C