Install Apple's iTunes software, wait for it to recognize the iPhone7 Plus device, and then click the "iPhone" icon at the top right.
Open the File bar in the upper left corner. Click the Add File to Repository option.
Open the folder where the music is located on your computer, select Import Music, and then click Open to import the music into iTunes software first. Imported music can be viewed in My Music in iTunes.
Click the recognized "iPhone icon" on the iTunes interface, and then enter music.
Select the "Synchronize Music" option on the right, and click to select "Selected playlists, artists, albums and genres".
Check the imported music, click Apply in the lower right corner, wait a moment, and the music will be imported into iPhone7. Turn on the mobile phone music and you can see the music.