You'd better upload the list and analyze what materials you lack. According to the instructions of the embassy, just send an email first. The title and content were issued in accordance with the instructions of the embassy. If there is no specific explanation, then the title of your email can be written as "email after being asked for XXX visa by the embassy" E-mail content can be written in the following format:
Dear Visa Officer of the US Embassy in China:
Hello! My name is XXX and my birthday is XXX. I applied for a visa to the United States on a certain day. The visa officer asked me to send an email to this mailbox, telling me that the visa lacked materials. Looking forward to your reply.
XXX
Because I don't know all your information and visa process, the above is for reference only.