Hi, welcome, it should be a red dongle on the left hand side of the ABS pump when looking at the front of the bike behind the 2 big green box fuses. Looks sort of like a USB plug. It should be given with the bike for free, or most previous owners just have it plugged in but if not, BMW sells them for like 30 quid and I think there is even some home made solutions using resistors that do the same job.
Wish many fun filled miles with the dongle of doom!