One way to do it is to give each student a different player from the Korean national team and they win prizes depending on how their player performs e.g. scores a goal, yellow card, red card, comes on as a sub. Each different category gets a different prize. If you want the gae to last longer in the whole tournament maybe choose a better country that Korea or use your home country (assuming they qualified) if that is more appealing as you will have to keep an eye on what happens yourself. We used to do this back at home through work using yellow card = white wine, red card = red wine, sub = 4 cans and a goal = a tenner. Not sure these prizes will work for you though! Different candies are probably best.

An alternative way is they get a raffle ticket each time their player does one of the above and at the end of the tournament have a big raffle draw.

Other side things to do are to guess the total number of goals scored or even which two teams will qualify out of the groups.