Go to Channel and Click on setting icon.

When you Click on setting icon, advance setting for selected channel will appear.

Go to Custom Image Click on Upload Button.

Click on any one Media Library/Icon

If you Click on Media Library,The Media Library page will be open.

Select Files and Click on Select Button.

The Uploaded image will be shown on the Channel Icon.

If you Click on Icon,The Icon page will be open.

Select Any Bootstrap Icon And Click on Insert Button.

The Uploaded Icon will be Shown On the Channel Icon.