I found this to initialize buffer in RenderGraphUtils.h
/** Creates a vertex buffer with initial data by creating an upload pass. */
RENDERCORE_API FRDGBufferRef CreateVertexBuffer(
FRDGBuilder& GraphBuilder,
const TCHAR* Name,
const FRDGBufferDesc& Desc,
const void* InitialData,
uint64 InitialDataSize,
ERDGInitialDataFlags InitialDataFlags = ERDGInitialDataFlags::None);
It works well.