Open the pack/dispenser and place it into an airflow. It will slowly evaporate and provide long-term lasting protection from infection, mould and unwanted odours.
It will also reduce CO2, and (BONUS!) act as an insect repellent.
Depending on the size of the room/strength of airflow, an appropriate size pack will last from 3 weeks to 1 month!
Clean the area
Place Gel in the A/C/FCU or any source of airflow