If you tap on the star icon (upper-right corner buttons) and then tap on the RESTART button, you will multiply your earnings and earn new boosters for your district. You could level up your district to earn more in-game money since you will have more fires to extinguish. However, there will be a moment that you could feel that you can’t progress in the game anymore. That means you should restart your city!
Once you reach the amount of in-game money detailed in the RESTART button, you will be ready to do Prestige in your city! The more progress you have in your districts, the better the prestige offer.
Take in mind that you will start your progress from scratch in this area but, at the same time, you will be able to progress further in the game: since you will receive higher money multipliers and better rewards, you will be able to unlock new vehicles, tech points, research, and in-game features. Don’t worry about your old progress! You will recover it really fast thanks to the new perks.