generic expand partition script for chromium os

hello, i found this topic and this issue regarding expand partition script, it works for me on raspberry pi, it seems this is developed by fydeos, not a generic script from chromiumos itself, as i can’t find it on image built for a different board

i’m testing chromiumos on a chromebook tablet booted from external usb, system also only uses 4g space, how to expand partition in this situation?