Been There Done That.... He should be able to completely shut off the bike and turn it back on and ride it and it will clear. If not off to the dealer.
Had a Yamaha Tenere for a bit, one way to trick the linked ABS and shut the system down (for dirt riding) was to run the bike on the stand. A wheels speed indifference is detected, bike assumes an error has occurred, turns on ABS light and shuts it down. Normally reboots the next time the bike starts. Enter diagnostic mode, clear any code and restart the bike.