DWM1001 - correcting distance error of +-20cm in code

Hi, how should I correct the distance error of ±20cm in the post-processing stage, meaning no recalibration of sensors?

It depends what you want to correct for.
If it’s antenna delay for TWR then simply subtract the antenna delay for both of the units used in the range measurement.
If it’s temperature then subtract then calculate the difference between the temperature when the unit was calibrated and the temperature when the range was measured. Multiply this by the temperature coefficient for your units (or value given in the application notes) and subtract it from the measurement. Remember to do this for both ends.

Not sure what you mean with “no recalibration of sensors”, but trimming the CFO using the xtal_trim register can also improve accuracy.

If you haven’t already, I suggest having a look at APS011: Sources of Error in Two Way Ranging.