Please read the followed FAQ for help:
M11 Plus LTD: https://forum.fiio.com/note/showNoteContent.do?id=202107010956367510284
M6: https://www.fiio.com/newsinfo/477750.html
M7:https://www.fiio.com/newsinfo/477747.html
M9:https://www.fiio.com/newsinfo/477746.html
M11/M11PRO:https://www.fiio.com/newsinfo/477748.html
M15: https://www.fiio.com/newsinfo/477751.html
How to wipe the cache & data in Recovery mode on X5 3rd gen/X7/X7MKII:
https://forum.fiio.com/note/showNoteContent.do?id=202107010951359479798&tid=21