Making yourself eat more will eventually increase your appetite. Your stomach has baroreceptors lining it that tell you you're full, so if you're not eating a lot now, then you are "told" you're full by your stomach. By eating more (not to make yourself sick), you will over time stretch your stomach.
Also, making yourself eat certain meals, like breakfast (a lot of people skip breakfast), not taking breaks or taking too long to take your break at work, etc., will over time increase your appetite.
It's like if you want to be more awake when you wake up, make your ass get up and get busy doing something, do that for a few days, and then you'll be more wide awake.