I have not done it yet, but this may help you get started:
There are two versions of the programming environments (board files) in Arduino IDE for this board. Version 1.0 is using Adafruit (RTOS) and libraries and version 2.6.1 using Arduino on top of Mbed. Cannot use both at the same time. Have to uninstall one in order to load up the other.
Here are some examples that Seeed says can be adapted to QSPI from SD:
There is an example already in the Arduino IDE under named “Adafruit Internal File System on Bluefruit nrf52” => “Internal_ReadWrite” that works. It’s a very simple program that allows you to name a file and some text that you want inside that file and it will write it. Then when you reboot/restart the board you can read back that text from that file.
Careful not to place any write functions inside the “main loop” or it could wear out your memory. I assume its true for QSPI also.