How to exhaust the warm air after BMW replaces antifreeze?

After BMW replaced the antifreeze, the warm air exhaust was realized from the small kettle tube in the water tank. The specific operation steps are as follows:

1. Press the brake pedal of BMW.

2. Press the one-button start button of BMW to start the engine.

3. Run the engine until the water temperature reaches 90 degrees Celsius.

4. Press the start button again to turn off the engine.

5. Let the engine cool naturally to normal temperature.

6. Pull the front cover to open the switch.

7. Lift the front cover.

8. Unscrew the lid of the kettle and let out the gas inside.

9. Add antifreeze to complete the operation.