Fixing a paint chip?

Hey all. As the title ask, I need to fix a paint chip on my ride. Not sure how or when it happened. But I was just walking around the car and noticed a chip on the top of the pass. fender. It is down to bare metal and has some rust. I painted the car last summer Plum Crazy and have the left over primer and paint still in the garage. What can I do? Thanks for any help.