It can be modified through the personal data setting function of mobile QQ. The specific steps are as follows:

1. Open the mobile QQ, and click the personal avatar in the upper left corner (as shown below):

2. Click "Dress up my QQ" (as shown below):

3. Click the "background" function (as shown in the figure below):

4. You can click the "Upload Background" function to set the pictures that come with the mobile phone album as the background, or you can find a nice background at the bottom and click "Dress Up Now" to finish, but most of the backgrounds provided by QQ are charged, so you can carefully find a small amount of free backgrounds (as shown below):

5. If you upload a background from your personal photo album, click a background at random and click "Next" (as shown below):

6. Adjust the size to your satisfaction, and then click "Dress up now" (as shown below):