If the router behaves erratically after an update, perform a hardware reset. Locate the small pinhole on the back or side of the ZLT P21. Use a paperclip to press and hold the button inside for 10 seconds while the device is powered on. This restores factory defaults.
: If your P21 was provided by a carrier (like Airtel, Globe, or Telkom), check their support pages. Manufacturer Support zlt p21 firmware update