The duty to help does not apply. However, the reviewer or judge will review whether VA fulfilled its duty to assist during your initial or supplemental claim.
But I have a particular circumstance, in my case I do not agree with a VA decision that I received in January 2019, what can I do in that case?
If you disagree with a VA decision you received before February 19, 2019, you can opt for the modernized review system after receiving a VA Statement from the SOC on the case or a Supplemental Statement from the SSOC on the case.
What if I want to choose a different review option after I have submitted a form?