Hello friend!
First of all, the HS8546V5 is a series of devices customized for China Mobile. We have no right to know your ISP customization requirements. The following operations are performed to establish an SSH access channel on the HS8546V5. However, I cannot guarantee whether the configuration is successful. If your ISP disables the feature, you need to contact the ISP for a solution.
1. Use the administrator account to log in to the web interface of the device.
2. Choose Security > WAN Access Settings. In the navigation tree on the left, choose ONT Access Control Configuration.
3. In the right pane, choose Enable LAN-side PC to access the device through SSH/Enable WAN-side PC to access the device through SSH.

The device can then be accessed through the SSH access tool.
Thanks!