It is possible to argue that Henry Kissinger really did not accomplish anything in Vietnam. He contributed greatly to the formulation of US policy in Vietnam in the Nixon Administration. He played a major role in the peace talks that led to the US withdrawal. But it is not clear that either of those things really accomplished anything.
Kissinger is most noted for his role in getting the US out of the Vietnam War. When Richard Nixon was elected, he promised to pursue “peace with honor” in Vietnam. He and Kissinger felt that they needed to extract the US from the war without making it seem like the US had lost and was retreating. Therefore, Kissinger helped to design the policy of massive bombing of the North that was meant to show that the US was negotiating from a position of strength. Kissinger then led the negotiations with the North Vietnamese. These negotiations led to the US withdrawing from Vietnam in 1973.
But did this accomplish anything? It is not at all clear. The bombing of the North clearly did not lead to American (or South Vietnamese) victory. The US left the war, but it is clear today that the US left because it could not win, not because it had accomplished anything. Therefore, you can argue that all Kissinger did was to maintain the pretense that the US was withdrawing on its own terms. This pretense rapidly fell apart. South Vietnam quickly fell and it is widely recognized today that the US lost this war. Therefore, Kissinger really did not accomplish much at all.