The Boveda Smart Sensor App provides a wizard driven process to calibrate your sensor. It utilizes the Boveda One-Step Calibration Kit using a 75% or 32% relative humidity standard. A one point calibration will only require the 75% RH standard while the two point calibration will require both the 75% RH and the 32% RH standards.
But if you have an external reference to compare the sensor against, you can use the Customize calibration feature in the App to manually enter an offset. Using the external calibration reference data and comparing that to the humidity reading of your sensor, the difference between the reference value and the sensor reading is the calibration offset. Enter that value in the offset field on the Customize screen.