Go to printing: in the right hand panel choose the top option: midweek meeting (this is chosen by default), then 2nd option: Assignment slips. Once you choose that an extra option becomes available: 'assignment slips for students'.
This only works if you have downloaded the S-89:
FIRST: define a custom template folder in Settings - General - Custom templates folder (this should not be TB's own template folder and should not be in the TB programm directory, because of permission issues). Put your downloaded S-89 in that folder. TB will do a conversion of the pdf to jpg.
Another way of handing out assignments is to use the copy button in the assignment dialogue. You can than mail/text/whatsapp the assignment.