Given that carbon dioxide is heavier than air, Is there any easy, inexpensive and simple way to use that fact to help people remove some of it from our homes and help improve air quality and cognitive function? I'd like to keep it at under 800ppm if at all possible!
Carbon dioxide (CO2) is indeed heavier than air, and you're correct that it can contribute to indoor air quality issues, especially in enclosed spaces. While there's no easy, inexpensive, and simple way to completely remove CO2 from your home, there are a few steps you can take to reduce its concentration and improve indoor air quality:

Ventilation: Open windows or use mechanical ventilation systems to allow fresh air to circulate through your home. This will help dilute the concentration of CO2.

Plants: Certain plants can absorb CO2 and release oxygen through the process of photosynthesis. Adding a few plants to your home can help improve indoor air quality.

Air Purifiers: Some air purifiers are specifically designed to remove CO2 and other indoor air pollutants. Keep in mind, however, that air purifiers alone will not be able to effectively lower CO2 levels to below 800 ppm.

CO2 Monitors: Installing a CO2 monitor can help you keep track of indoor air quality levels and determine when it's necessary to open windows or use other methods to improve air quality.

It's important to note that CO2 levels in enclosed spaces can quickly rise to harmful levels, particularly in the presence of people who are exhaling the gas. So, it's important to regularly ventilate enclosed spaces and monitor CO2 levels to ensure a safe and healthy indoor environment.