If the flex in question is the one that runs underneath the heat shield and connects to the logic board )see Step 44 of this [guide|111373|Guide|stepid=213511]), then the only way to replace it is to replace the entire screen assembly.
+
If the flex in question is the one that runs underneath the heat shield and connects to the logic board (see Step 44 of this [guide|111373|Guide|stepid=213511]), then the only way to replace it is to replace the entire screen assembly. The little nub that connects to the Home Button Flex goes underneath the backlight and connects with the rest of the flex assembly which connects to the board. That flex cannot be replaced.
If the flex in question is the one that runs underneath the heat shield and connects to the logic board )see Step 44 of this [guide|111373|Guide|stepid=213511]), then the only way to replace it is to replace the entire screen assembly.