Accessing USB on Android by using blueprint

Hello,
I’m developing an Android game. I want to write/read a simple *.txt file from an external USB device. While testing the app on Windows, I can write the USB directory as “H:\asdf.txt” etc. However, I couldn’t find what to type as an address for an Android device for the same function. I will always use the same device, so no worries for other devices and other android versions. Is there any way to find out USB directory for my specific Android device to set it as a string variable for my bleuprint.