Houseplants do not exchange anything near significant amounts of CO2 for this purpose.

The long term answer is to improve the HVAC: reconfigure for more external air mixing (commercial), or find a way to install an HRV or ERV, or open a window, but that can be expensive or impossible depending on the situation.

The houseplant was just the cheer them up while they slowly suffocate since they weren't going to do anything about it.

Like a button that does nothing.

I'm currently renovating a house in The Netherlands, we're installing a heat pump and to make the place more efficient we also replaced the glass with triple glazed (but without vents in the frames as they let heat escape). Given that we were effectively making our house a "sealed envelope" we had to add mechanical ventilation (ERV) to ensure proper airflow around the property. As you can imagine, retrofitting ducting around an old house required a LOT of creative work!

> If it is CO2 then you could invest in a houseplant or two.

This seemed wrong to me, so I checked and it seems like you'd need hundreds of houseplants to make any significant difference: https://www.realhomes.com/news/do-house-plants-remove-carbon...

Seems like there'd be a market for a CO2 > O2 exchanger of some sort. I don't know enough chemistry to recognize why this is probably too difficult for commercial viability.