Dont know about X5 but other BMW mirrors..
First you nead to remove the glas on most BMW it is held by few clips, carfully tilt the mirror glas to the side and take a peek and se where the clips are take them out one by one going in circle, when done dissconect wire for heating and or any other wires. Now you should se more clips that hold the black frame att the front, remove them and remove the black frame. Now some more clips that hold the back of the mirror (where the lamp is located) remove those as well. Now you should se what you are looking for
PS. This is how mirror is mounted or dissmounted on the X3

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X5 4,4i-06 Current
330Ci Cab-03 2007-2008
MB E55 AMG-03 2006-2007
Z3 2,8 Roadster-98 2006-2007
X3 2,0d-05 2005-2006
320d-99 1999-2005