all China can do is kill the value of the dollar against CNY, which it probably doesn't want to do, because both for domestic growth and geopolitical reasons, it wants to sell to the US, not price out US consumers. changing the status of USD would take coordinated multilateral change.

(It could I guess play games and sell USD for EUR or something, rather than CNY. But then Europe would respond to the unwanted appreciation of the Euro. Ultimately China's trade imbalance is a hot potato so far only the US has been willing to swallow.)