Some common reasons for restarting Mysa include; Mysa has disconnected from the WIFI and is having a hard time reconnecting, the temperature is showing higher than it actually is, settings are not being saved, etc. To reboot your Mysa, hold down the 'Down' arrow for 15-20 seconds. It will lower the temperature and then enter off mode, represented by the dashed line. Keep the arrow down until 'RT' appears on the display. Let go of the arrow, and the thermostat should reboot and display the smiley face.
If that doesn't work, you should try to power cycle the thermostat by turning the breaker connected to the thermostat off then back on again.