Press the multitasking key, and in the multitasking interface, slide the application thumbnail to the left or right, or click the "X" on the upper right of the application thumbnail to close the application alone.

Or click the trash can icon to clean unprotected (locked) applications in the background at one time. If you don't want to clean up the application, you can click the lock icon in the upper right corner of the application task card. In the future, when the background application is cleaned at one time, the locked application will not be cleaned.