China implements foreign exchange control, and foreign currency cannot be automatically converted into RMB, but foreign currency holders are required to "settle foreign exchange" in the bank, that is, the holders need to explain the source of foreign currency, such as export payment, so they need to settle foreign exchange with the customs export declaration form, which is labor income, so they must provide labor contracts and other documents to prove legal income, otherwise foreign currency cannot be converted into RMB at will.

If it is a dual-currency letter of credit, you can check foreign currencies at the ATM, such as RMB and US dollar dual-currency credit cards, and then the ATM can check whether there is US dollars in the card.