In this youtube video I explained how to transfer files from computer to the board using NuttX:
https://www.youtube.com/watch?v=Ne3SZZrwL9c
But it is possible to transfer files from the board to the computer, ie:
nsh> sz -d /dev/ttyS0 -r data.db -x 1 -o 0 /mnt/esp/wifi/data.db
When you run this command the minicom automatically starts receiving the file.