Corruption cannot be eliminated completely, but you can reduce it significantly.
In order to fight corruption, you must invest money in police by increasing its funding. This will help you make corruption grow slower.
If corruption becomes uncontrollable, special large-scale operations are needed. To carry them out, go to the police screen and press the handcuffs icon: the operation will begin, the guilty ones will be arrested, and the corruption level will decrease.
Don’t forget that corruption lowers your revenue per second. Some part of the revenue is not contributed to the budget. If the corruption level reaches 100%, your budget will cease to grow, all the money will be stolen, and the need for urgent special operations will arise.