Mark's answer is indeed the library you want.
In Arduino IDE, first select Teensy in Tools > Boards. Other menus update depending on the selected board.
Then click File > Examples > SPIFlash > SPIFlash_ReadWrite.
Libraries LittleFS and SerialFlash also access this type of chip, but those libraries emulate a filesystem. The SPIFlash library is meant for raw access directly to the chip without any filesystem layer.