A hard reset is easy, the problem is that when should you decide a hard reset. A hard reset takes around 1 minutes.
To do a hard reset in MiFi, just do this.
First upgrade to v2.22, which is available here: GL.iNet download center. The control GPIO-LED name is a different
echo 1 > /sys/class/leds/gl-mifi:usbpow/brightness
sleep 1
echo 0 > /sys/class/leds/gl-mifi:usbpow/brightness
just wait and the the network should connect using the same settings.