If I was in that situation I would consider opening the windows twice a day for 15 minutes, then running a good (and properly sized) air purifier on full blast for an hour.
The sibling comment is right, it doesn't help very much. The COâ‚‚ level goes above 800 ppm (which is already considered unhealthy) in ~20 minutes, rises to ~2200-2400 ppm (depends on wind speed and atmospheric pressure) in the course of a couple of hours, and then just stays there for days on end.
I put all my pollution data into Grafana and it makes making decision when to open (or close) a window that much easier. (Yeah, you have to make a thought-out decision to not feel terrible. It's a whole ceremony.)
Depending on the size of your house/apartment, you'll use up that oxygen in a couple of hours and will be back at 1000+ levels. Plus, there must be some ventilation in OP's setup already, as the CO2 levels are at 2000, and without ventilation they'd just rise until he passes out...
