Set the icon and splash screen like this:
# (str) Presplash of the application
#presplash.filename = %(source.dir)s/data/presplash.png
presplash.filename = chart.jpg
# (str) Icon of the application
#icon.filename = %(source.dir)s/data/icon.png
icon.filename = chart.png
Remember to 'buildozer appclean' after the change and before the next build.
If you have a problem check that the image file types are supported for the case.
For more control of the presplash use lottie files
# (string) Presplash animation using Lottie format.
# see
https://lottiefiles.com/ for examples and
https://airbnb.design/lottie/# for general documentation.
# Lottie files can be created using various tools, like Adobe After Effect or Synfig.
#android.presplash_lottie = "path/to/lottie/file.json"
I have no experience using lottie files.