Is it possible to set the automatic restart of the device once in a week or month...

SIBIN

At many of our installs, we are facing issue with lower speed, delay in getting IP for the new connected device and it is resolved once the controller is restarted.

Zyxel_Joslyn

Hi,

Would you like to trace this problem? If yes, could you help to collect the diagnostic when you feel the issue occur?
Here is the steps and CLI to force the controller to reboot.
1. Please extract the attachment and upload the .zysh file to the MAINTENANCE > File Manager > Shell Script. 
2. Apply the CLI via SSH or console.
Router> configure terminal
Router(config)# schedule-run 1 reboot.zysh <daily/monthly/weekly> <time,HH:MM>
Router(config)# write
The controller will reboot at the timing that you set.
Thanks.

Joslyn