First, lift the assembly from the back (green arrow), while keeping the front clear plastic part resting on the springs (red circle).

Then, while pulling it toward the back very slightly, carefully lift the front part off the springs.

The clear front part has a hole that attaches onto a clear nibble just below the bracket (blue arrow in second picture) for the scrollwheel to pivot left and right for the left and right scroll function.

Though the pivot point isn't attached too deeply. When reassembling, align the circular marks in the front to the springs, then press the back side down into the holder and it will self align.

Remove the springs and keep them safe.