Here's a breakdown:
* Repairing a single switch: Highly unlikely. The switches are usually surface-mount components soldered directly onto the circuit board. Accessing and repairing them would require specialized soldering equipment and skills, and even then, success isn't guaranteed.
* Replacing a single switch: Almost impossible. The switches are not individually replaceable.
* Replacing the entire assembly: This is the most common and practical solution. You can find replacement switch assemblies online (e.g., eBay, Amazon, auto parts stores) relatively inexpensively. The difficulty lies in the installation, which requires some mechanical aptitude. You'll need to remove the door panel to access the switch assembly.
In summary: While technically you *could* try to repair a single switch, the effort and specialized tools required usually outweigh the cost of simply replacing the entire switch assembly. Replacing the whole assembly is the recommended approach.