To clean your foundation brush, you can follow these steps:

1. Wet the bristles of the brush under warm running water.
2. Apply some soap or cleanser to your palm or a cleaning pad.
3. Swirl the brush on your palm or cleaning pad to loosen up the debris.
4. Rinse the brush until the water runs clear.
5. Repeat the process if needed.
6. If you use an oil-based foundation, you can add some olive oil or coconut oil to your soap to help break down the makeup. This is also good for natural brushes.

It is recommended that you clean your makeup brushes every 10 uses. This will help maintain their performance and ensure healthier skin and better makeup application.