You probably don't.
Arbitration awards generally can only be reversed under very limited circumstances, and your delay in trying to do so is another reason why your attempt is looking very challenging. To learn more about modifying/vacating an award take a look at NRS 38.242-43 (Nevada arbitration law) and 9 USC S 10 (federal arbitration law).
More information would be helpful. Assuming your case was in the court annexed mandatory arbitration program, you can file a request for trial de novo. Your case will be put in the short trial program unless you remove it. There deadlines are fairly short, so you may need to act quickly. You might also want to discuss your case with an attorney.
There will need to be some very unusual circumstances if it has been years. Your best bet would be to talk to an arbitration attorney to see if there is any possibility.
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