The cable connecting them may just be loose, you can get the service manual easily from Dell's website. If it is a hardware failure then I believe you have to replace the palmrest assembly, which is easy enough. The instructions would also be in the service manual.
Internal Parts And Assemblies
There's a link to your parts list, the palm rest assemblies are about halfway down. Just take any of their part numbers and search them on ebay to find the cheapest place to buy from. Probably won't cost more than $30 all together.