FiiO M11 Plus Portable High-Resolution Lossless Wireless Music Player - Manual (Page 98)

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3) Do not manipulate the device during the upgrade.
2. Force to reboot
If something wrong that happened to the device (stuck in the Welcome page, no
response, etc.), you can hold the Power and the Play button together for 10
seconds to force it to reboot.
3. Factory data reset
If there are some problems happened to the device, perform the factory data
reset would help (In the menu of Settings->System->Reset options).
Notes: The "Factory data reset" will erase all data from the internal storage and
reset the device to defaults. Please backup corresponding files in advance.