My dentist said i might need root canal. is there a way that i can reverse tooth decay?

Not in this case: Very, very small caries that have begun can be reversed with special remineralizing toothpastes. If your dentist said your cavity is that deep, then be prepared for the root canal, and be more diligent in caring for your teeth in the future to avoid these problems.

Not at that level: Only incipient(very initial stages) decay can be reversed. If you are considering a root canal, your decay is far beyond reversal. You have two choices: root canal therapy or extraction.

In its earliest form: It is possible with Fluoride application. But once it progresses in or near the nerve the answer is no it is not possible.

To little to late: Tiny incipient loss of enamel integrity can be modified with Fluoride or remineralization agents. Large areas of infection, large cavities that infect the nerve of the tooth, are not reversible. Get the root canal done and work with your dentist to prevent this from ever happening again. This isn't a diy project, you need skilled professional help.