Cobra F6+ ? It has no removable back weight ! If you are talking about the smartpad, it's not designed to be removed. Cobra F6 has a removable back weight but not the F6+.
If you're talking about the sliding part grooved into the track, it's not designed to be removed. At least I had not tried to remove it. Why would you want to remove that part ? You change the weight by changing the the top which is color coded. http://www.cobragolf.com/king-f6-weights