Looking underneath from the rear you will see the lower suspension arms. The camber adjustment is located at the inboard ends closest to the differential. To reduce camber, two spanners are required. Loosen forward nut and adjust camber by rotating rear bolthead until fat part of cam is toward the tyre. This is minimum amount of camber achievable (reduces wear on inner edge of tyre). Make sure the bolts are tightened adequately when finished. Some people worry about loss of cornering performance with reduced rear camber, I have not noticed any difference. I had an alignment done on my X5 after I adjusted the rear camber to its minimum, the resultant camber was still within worshop manual specifications.
Good Luck
Colin.