When you start the sensor, you need a run in time.
The default mode of UI is using ULP mode (300s time interval) to get IAQ value. this means the run in time needs about 20 - 30 minutes at least.
Also you can expose sensor to different environment (clean, poluted, clean) to get the calibration status increased from 0 to 3.
You can put sensor in each environment for around 10 minutes.
When the sensor is turn on, and you run sensor to accuracy level 3, then you can store all the parameters.
We have such API in the integrate guide of BSEC.
Then next time you turn on the sensor, you can restore those parameters.
Sensor will start from 3 directly if the environment has no significant changes.