[Vuejs]-Quasar Framework: How to use a different icon set with QUploader

Use Slots:

In the example below we’re showing the equivalent of the default
header.

Check the Official Documentation, in the Custom Header you can customize the icon.
https://quasar.dev/vue-components/uploader#example–custom-header

Edit:
Looks like you have to change the Icon Set in the configuration file, here a video from Luke where shows the process,
https://quasarcast.com/quasar-getting-started/quasar-getting-started-guide-3-skeleton-part-1