Basically, do as it says, you have to achieve a score of 3,450,000 or more after playing all levels on Hoth. You can’t just play any level and achieve a basic score and have it count towards the achievement. It’s going to be based off of all of your top scores combined.
I recommend to watch walkthrough videos on each level to learn how to better your score. A lot of the scoring is based on luck, in some instances you might find yourself resetting a level 100 times to achieve a better score, sometimes, only by a few hundred points or less. Which of course is better than nothing. This particular achievement is pretty difficult though. When I finished Tattooine, I was only off by 80,000 points for the achievement and was able to get the score I needed within a couple hours of playing. I finished the Death Star levels with more than I needed and didn’t need to go back and replay. With the Hoth levels, I was off by over 120,000 points when I finished and 3 starred all levels.
It can get difficult, but just watch walkthroughs and give it your all! In no time, you should achieve it!
If you find yourself getting agitated towards your attempts, remember there is an achievement for playing the game for 30 hours, so your working towards that as well... :)
Happy playing!
- Jon