fatal error: SerialFlash.h: No such file or directory

[GazzaH1]

Hi guys
Extremally new to coding. Have only come across this video as my daughter is getting married and said she wanted an audio guestbook phone so though I would give it a go. Have followed everything in the video and copied the code into Arduio but when I go to verify it I get this fault code coming up. I have no idea where its gone a miss as far as I can see in the code it doesn't reference SerialFlash.H anywhere?? Any help would be greatly appreciated as the wedding is next week. Note I haven't yet done the addition updates to the Boards and Platform text files as my laptop is locked out and I need to get the bloody administrator crap taken off it tomorrow by my IT company I use.
Fault code coming up as per below.

Arduino: 1.8.19 (Windows 10), TD: 1.58, Board: "Teensy 4.0, Serial, 600 MHz, Faster, US English"

Multiple libraries were found for "SD.h"
In file included from C:\Program Files (x86)\Arduino\hardware\teensy\avr\libraries\Audio/Audio.h:129,
from C:\Users\Gary Harrison\OneDrive - TNTL Heavy Equipment Repair\Desktop\sketch_Wedding_Audio_Book\sketch_Wedding_Audio_Book.ino:25:
C:\Program Files (x86)\Arduino\hardware\teensy\avr\libraries\Audio/play_serialflash_raw.h:33:10: fatal error: SerialFlash.h: No such file or directory
33 | #include <SerialFlash.h>
| ^~~~~~~~~~~~~~~
compilation terminated.
Used: C:\Program Files (x86)\Arduino\hardware\teensy\avr\libraries\SD
Not used: C:\Program Files (x86)\Arduino\libraries\SD
Error compiling for board Teensy 4.0.

[cp1797]

You need to add the library through Tools -> Manage Libraries and look for SerialFlash