The first thing you'll need to do before addressing any oil can such as that, is to figure out what caused it. There are two kinds of oil cans, a loose oil can and a tight oil can, and they use different methods of repair. Pick the wrong one and you just compounded your problems....
A loose oil can may be caused by either welding, which causes a shrink of the immediate area, or fatigue of a panel over the years may cause a panel to loose some of it's shape to hold the crown (think of an old car hood, no damage but sometimes they can get floppy), or other outside forces, as will be explained later. The loose oil can is noted by a panel that easily flops back and forth.
A tight oil can is one usually seen as a result of body damage, a dent or glancing blow will take the crown that the panel used to have, and push those forces elsewhere. The oil can is noted by a tight flop. In other words, you can push it one direction but it will require a bit of force, and then when released will typically spring back to the original position, but not in all cases.
It is crucial to determine which you have as they use opposite repair methods. The loose oil can will need to be stretched to restore the crown of the panel, the tight oil can will need shrinking to remove the excess panel shape caused by the dent or body damage.
Where the long crease shown on your panel leads one to believe there is a tight oil can there, it is also possible to have multiple oil cans in on panel. For example (NOT saying this has happened in your case, only a possibility to verify) the crease you show causes the immediate area to stretch and displace the original crown into other outlying areas. This may include pulling the crown down from an adjacent area into a loose oil can. So in this example, you would have a tight oil can caused by body damage that induced a loose oil can by pushing the forces that hold the shape of the panel into other areas. The point of all this rambling is that first caused the second. In this example you will typically correct the issue in the loose oil can by fixing the tight oil can which is what caused it. So we would leave the loose oil can alone and shrink the immediate area of the crease caused by the side swipe.
The other possibility is that you have multiple dents. One is a side swipe crease, the other caused from a direct blow, whether a softball injury, a bumper strike, or other outside forces to stretch the metal. Both in this case would need shrinking.
This has not been written to tell you what has occurred there, but to give some possibilities only. Now you need to look a little closer and determine if in fact the low spot is a dent or caused by displaced forces from elsewhere. The repairs to correct are two different methods. (yes I've repeated that a few times, it was intentional)
I've got my thoughts on what has occurred but don't want to sway yours. Besides, it's difficult for anyone to tell you what you have there over a computer monitor three thousand miles away without knowing how those areas react to pushing/cycling the oil can, etc.
