From the data sheet, the Si7020 claims that it is a precision relative humidity and temperature sensor, the accuracy is ± 4% RH (max), 0–80% RH and ±0.4 °C (max), –10 to 85 °C respectively, with operating ranges of 0 to 100% RH and –40 to +125 °C.
The DS1820B has an operating temperature range of -55°C to +125°C and is accurate to
±0.5°C over the range of -10°C to +85°C.
Neither is capable of calibration.
If you search the old forum (especially), I’m fairly certain that there are details of the method to check the calibration of the humidity sensor.