Hi @thibaultb473199 ,
Does you instance has any Business Unit created? If yes, then look for table 'business unit' and add new BU names there.
If not, then you need create one schema where you can enter names of different 'business unit'. Also, each recipient will be associated with one business unit, so create link between 'nms:recipient' & 'businessUnit' tables.
Thanks,
Jyoti