sensor goes down to zero , so 0 becomes new "baseline" - while otherwise working normaly - recalibration

[viisauksena]

we succesfully applied the sensor to a nodemcu - it was working fine.
Then we walked to another house nearby (with sensor/nodemcu still running on battery)
(loosing wifi for short amount of time, and moving to high humidity cold outside, in warm inside again)

the sensors value moved to zero, we have no clue why.
if we exhale near to it , it is showing quite reasonable values (1..2..3000 ppm) - so we assume it is working normaly. humidity and temperature still working normally.

i am not sure what we may have done to get this "false readings" - or at least - zero base value thingi.
is there a way to start some kind of calibration, may i ask for a sufficient arduino-code-snippet.
or do someone have any other inside what may have happened, and how to bring the sensor readings back to normal.
We also have other sensors here still working fine. (and we can use them to compare values)

[viisauksena]

the autocalibrate didnt help,
here a snippet that helped (we had a second sensor to calibrate)

• i used forcedrecalibration with a known value and let it run for some minutes ; then reflash without forcedrecalibration

  // autocalibrate - they say let it run for 7 days , 1 hour "fresh" air daily - not very reliable i guess
  // seems best to even avoid this setting at all
  // airSensorSCD30.setAutoSelfCalibration(false);
  // calibrate ... run once with a known co2 level (like from another sensor)
  // reupload without forced recab - should remember actual correctness (whatever that may be)
  // this seems to work 
  // airSensorSCD30.setForcedRecalibrationFactor(790);