Gyroscope calibration is performed automatically the first time the firmware is run on the hardware. For nRF6937 product example and nRF6932 add-on, it is also possible to trigger gyroscope calibration by holding the orange button between Channel + and Volume + buttons for three seconds.
Smart Remote 3 firmware performs initial calibration on the first firmware run, but if you experience that the cursor is moving involuntarily when you start using the free-space navigation, this is due to gyro wandering. The SmartMotion® firmware library will automatically compensate for this movement. Simply leave the Smart Remote on a flat surface with free-space navigation enabled. After a few seconds the cursor will stop moving and you can pick up the Smart Remote and start using the free-space navigation feature.