If you've exhausted the software solutions such as reinstalling drivers and/or Windows itself, you may have a hardware problem. As nearly as I can tell, the trackpad comes with the palmrest/top keyboard cover as a single part if you buy it from Dell.
[link|https://www.dellpartssource.com/products/dell-latitude-e6220-palmrest-touchpad-assembly-w1j7h.html|Dell Latitude E6220 Palmrest Touchpad Assembly - W1J7H (A)|new_window=true]
It doesn't look too difficult to replace; here's a YouTube video showing how.
[link|https://www.youtube.com/watch?v=_RWEionhkU0|Dell Latitude E6220 Palmrest Touchpad Video Tutorial Teardown - YouTube|new_window=true]