is this the image that you see in your app which you want changed?
If so then you probably want to fork openedx-app-android and edit the images at app/src/main/res/mipmap-*
This is just a best-guess from me though, I haven’t actually put any effort into testing out the app so not sure if I’m even looking in the right place. I’m sure someone else will be better positioned to answer but maybe that puts you in the right direction at least… Perhaps the plugin maintainer @Abdul_Muqadim might be able to assist?