SEN0159 Sensor

Hi, I am using the Gravity: Analog Electrochemical Carbon Dioxide Sensor (0-10000 ppm) SKU SEN0159 Co2 Sensor 

for my Greenhouse Monitoring Project,

I would like to enquire that I am connecting the sensor, with the Analog pin on the A0 pin of adc port of grove base HAT, which was attached on the raspberry pi, however, the ppm I read in indoor (my room) is around 2000-4000 but sometimes increase till 10,000, where it keeps on fluctuating, and the ppm output seems to be much higher as in a

 room, but for the callibration mentioned in the code where to find the REACTION_VOLTAGE when at 1,000ppm environment, point is I couldnt find any places with such known concentration for me to test as a student, thus, for now the problem is the accuracy problem and reading fluctuating problem, attached below is my code and the data of co2 detected, can anyone help to check what is the problem?