When you disagree with the VA decision on your claim, a Supplemental Claim may be filed when you submit new and relevant evidence. New evidence is information you didn’t submit to the VA in the past. Relevant evidence is information that proves or disproves something in your claim. A Nexus Letter with an Independent Medical Opinion from Veterans Audiology meets this VA criteria.

https://www.va.gov/decision-reviews/supplemental-claim/file-supplemental-claim-form-20-0995/start