If cleaning didn't help you'll need to get your system to an Apple Store for repair. Given the age of your system I would think it would be under warranty.
There is no IFIXIT guide for the retina models to remove or repair the Trackpad due to the fact you will destroy the battery in the process!
The best I can offer you is this IFIXIT image of the trackpad on a different model: [https://d3nevzfk7ii3be.cloudfront.net/igi/FvtnBP15SIGyLAkT|Trackpad]. Here you can see the adjustment screw which is the large head screw on the left side. The screws circled are the ones you would need to remove to fully remove the unit.
Again this is a very big job as almost everything needs to be removed to get to the trackpad.