You can set the QQ group avatar in the following ways (as shown in the figure below):

The QQ version of mobile phone is the latest v8.9. 10.668.

1. First, open the WeChat group chat and click "Three Columns" in the upper right corner (as shown below):

2. Slide down and click "Manage Groups" below (as shown in the figure below):

3. Click "Edit Data" at the top (as shown in the figure below):

4. Click "Group Avatar" (as shown in the figure below):

5. Click "Change Avatar" (as shown below):