Adding new fresh air
You need to replace existing air in the premises with new fresh air, removing pollutants, VOC and CO2. At the same time, you must be cautious about the fresh air you bring into the building. Depending on where the building is located, you need to ensure the correct filter protection to manage potential outdoor pollution and not forget to replace them on a regular basis.
For certain premises where a lot of people are gathered in the same room at the same time, like waiting rooms, conference rooms etc. it could be wise to add extra filtration for that room alone to manage possible viruses to be spread.