1. Download the Recording Expert app and open it, click the edit button at the location below, as shown below:

2. Find and click the soundtrack button on the editing page, as shown below As shown:

3. Click the first button (select a music from the music library), as shown below:

4. Click the second button, as shown below :

5. Click the search button, as shown in the figure below:

6. Find the desired background music file by keyword, as shown in the figure below:

7. The third button below the main soundtrack interface can select the recently played recording file as the background music, as shown in the figure below:

8. Click the mix button to complete the soundtrack, as follows Pictured: