You can file a reopened claim for a benefit that VA previously denied if a year has passed since your claim was denied and you did not appeal that decision. However, VA cannot reopen a claim without new and material evidence.
"New evidence" is information about the claimed benefit that the VA has not previously considered.
"Material evidence" is information that is relevant to and has direct bearing on the specific claimed benefit.
A Veteran was treated several times during service for pain in his right elbow. He filed a claim for service connection, but his claim wasn’t granted because when the Veteran was examined the VA doctor didn’t find a problem. Two years later, the Veteran’s elbow was x-rayed by his private physician. His doctor found arthritis. The Veteran applied to reopen his VA claim, sending in his private doctor’s exam results – new and material evidence. Because the recent exam suggested his current elbow pain was an after-effect of his in-service elbow problems, VA reopened his claim.