Air Quality Sensor - SGP40 (Qwiic) Hookup Guide
El Duderino, MAKIN-STUFF 
Troubleshooting
VOC Index Data
The example in the Arduino library returns values processed through Sensirion's VOC Index which returns qualitative data based on the history of the room. While the sensor reports valid VOC readings within a minute of power up, leaving it running to gain a "history" of the room will provide more accurate data from the sensor when VOC events occur. In our testing we found the longer the SGP40 remains in the room it monitors, the more reliable the data becomes.
After acclimating to the room it is monitoring, the SGP40 should report "100" or close to it for the normal VOC Index for the room. Values below that indicate a lower concentration and values above indicate a higher concentration. Refer to Sensirion's VOC Index for Experts document as well as the SGP40 Datasheet for more information on how to interpret and use that data in your air quality measurement application.
Quick SGP40 Test
If you're looking for more accurate testing than using common household items like isopropyl alcohol or a permanent marker, Sensirion has a quick test document for testing the SGP40 is operating within specifications here: SGP40 Quick Testing Guide
General Troubleshooting and Technical Support
If you need technical assistance and more information on a product that is not working as you expected, we recommend heading on over to the SparkFun Technical Assistance page for some initial troubleshooting.
If you don't find what you need there, the SparkFun Forums are a great place to find and ask for help. If this is your first visit, you'll need to create a Forum Account to search product forums and post questions.