Here's what your options are:
* Professional Repair: The most reliable solution is to take your vehicle to a qualified automotive electrician or a specialist in instrument cluster repair. They have the tools and expertise to diagnose the problem (which could be a faulty sensor, a problem with the cluster's circuitry, or even a failed odometer motor) and perform the necessary repairs. This is likely to be the most expensive option.
* Replacement Instrument Cluster: If the damage is extensive or the repair cost is prohibitive, you might need to replace the entire instrument cluster. This requires finding a used cluster with a matching VIN (Vehicle Identification Number) or a new one from a dealer (expensive). Even with a used cluster, there's the issue of potentially mismatched mileage. This is a complex process that should be done by a professional.
* Dealing with the Problem: If the odometer is simply not displaying correctly but other functions of the instrument cluster are working, you might consider simply living with the issue. The mileage might be recorded elsewhere in the vehicle's computer, and that information is usually more important for service records. Depending on the nature of the problem (a stuck odometer, for instance), you might be able to track mileage in a separate logbook.
Important Legal Note: Tampering with or attempting to alter an odometer reading is illegal in most jurisdictions. If you are attempting to repair it to change the odometer reading, this is fraudulent and can result in serious legal consequences. Focus on legitimate repair solutions, not on odometer manipulation.
In summary, do not attempt to repair the odometer yourself unless you have extensive experience with automotive electronics and repair. The risk of causing more damage far outweighs any potential benefit of DIY repair. Contact a professional for the most reliable and legally sound solution.
