Telesur TV has the article $2B Nigerian-Chinese Currency Swap is ‘Win-Win’ Deal: Experts.
Just to be sure you understand what is being swapped, here is an excerpt.
The swap, totaling 15 billion Chinese yuan for 720 billion Nigerian nairas, or vice versa, aims to facilitate bilateral trade and investment and can be extended by mutual consent.
This isn’t necessarily a direct example, but I think it does show that China is not hemmed in by the $3 Trillion it has in US dollar reserves. The theory is that China can’t put that $3 Trillion to use without buying USA goods. If one of its trading partners is being pressured by lack of dollar reserves, I bet China could spare some to bail them out.