They could sell it back onto the open market and convert it to USD. Alternatively they could wait for it to mature and get USD.
The key thing here isn't about the reserves, its how they they acquired them by creating a swap on USDCNY from Chinese exports from their reserves - effectively holding the Yuan from appreciation.
The other thing is for the trade deficit to decrease the reserves need to decrease too. The reserves, especially the way they were created using swaps give a proxy of USD held savings held but not yet poured back into the US (and hence creating a trade deficit).
This is all of course useless if the holder of those bonds is still China, but through another country such as Belgium with an overseas account - which they've done before.
Thats assuming the EU isnt easy to buy off - looking at a couple of regulations in the pesticide industry its easy to see they're very accommodative. Lobbying is big business in Brussels.
Needs to always be on
Needs haptic feedback