Can you provide the make and model of the PC or the motherboard? This information can help in identifying where you can add a fan.

Look inside the PC case and try to locate any open spots or connectors on the motherboard where you might attach a fan. You may also check for any fan headers on the motherboard, which are typically labeled as "SYS_FAN" or "CHA_FAN."

If you can't find any available fan headers, you might need to use a molex adapter. This allows you to connect the fan directly to the power supply, although it won't provide fan speed control through the motherboard.