A Higher-Level Review (HLR) asks a senior VA reviewer to take a fresh, de novo look at the exact evidence already in your file. You cannot add new evidence in this lane, which is exactly the point. You use it when the evidence was sufficient and the decision was still wrong.

The informal conference

You (or your representative) can request a one-time informal conference with the reviewer. This is where cases are won. It is your chance to point directly at the duty-to-assist error, the ignored favorable evidence, or the misapplied rating criteria.

A difference of opinion is enough

Under 38 CFR §3.2601, the reviewer decides the issue de novo and can grant on a difference of opinion. You do not have to prove a "clear" error, only that the decision got it wrong on the evidence VA already had. The rule cuts one way: the reviewer cannot change the decision against you on a difference of opinion alone. That takes clear and unmistakable error, and any favorable finding already made is binding under §3.104(c). If the reviewer finds a duty-to-assist error that existed when the decision was made, for example the VA never ordered an exam it was required to, §3.2601(f) sends the claim back for correction and a new decision, and your effective date stays protected.