Been there, done that
They only show pictures of the ground cables in a row. No mention of where they go.
I even went to the BMW dealership and their parts department was unable to tell me due to their software only showed pics of the cables as well with no mention of location.
Luckily someone reached out to me with a rough general location of where it goes. Based on that I did find a hole where it might go, although there was plastic around the hole, so that seems to be a barrier for a good ground. I used it anyways hoping the inside of the hole (threads) is all metal. So far no issues....fingers crossed.