Refusal to calibrate suggests that handheld calibration may not have been correctly carried out recently.
A full calibration (low then high) should therefore be carried out using PC software.
If you do not have the PC software, it is available for download at https://www.analoxgroup.com/products/aspida then click <Software> and <Aspida - PC Tool >.
I recommend carrying out a full PC calibration ensuring advanced settings is selected and local atmospheric pressure is correctly entered.