I have a problem with my shifter. My bike is using Shimano Revo Shift(gripshift) RS-35 (see my picture). The one shifting the front derailer (the left shifter) does not click when I turn it but it can still shift the cable. How do I repair it? I don't even know how do open up the shifter in the first place.

![Shimano RS-35](https://i.stack.imgur.com/lJ8gL.jpg)