After installed the DLC, when you are in level, you can find a setting of "Speed x2" in the Pausing panel.
Notice: if you set the game speed to x2, all of the speed will be set to x2. If some levels also have the x2 effect, then it will became x4. So, it's will make game more exciting but more difficult.
Please note: Before installing the DLC, please update the game to the latest version

More details on the official game page of Game Speed x2 ...