(I just found this below online these are not my words but its been a while since we had to do this and I believe its correct. Your service menu access code below maybe different depending on your firmware.
has your printer had a big temp change in the past week or so? I know we sometimes would have codes thrown in the morning when it was cool but it would not happen in the evening when the building was warmed up.)
Turn off machine
Hold down Left, Up and Right arrows while restarting, press enter...
this should disconnect the tool carriage from the print head and it will ask 'align head' (can't remember if you press enter again now or after the next step...but you will figure it when you do it)
then slowly push the tool carriage all the way to the left - until the knife is activated
the press enter and the carriage will come back to the print head and reset the whole unit and turn off
Turn machine back on and should be all good to go