Hello. I'm from colombia and currently I'm working in the USA. I already paid the fee to give the biometrics for the visitor Visa. I have the appointment the 21st of November but I can't go that day to the ASC because my work's schedule change and I will not be able to go. How can I ask for more days and where can I send the letter or explanation for it. I really appreciate if you can give me a link or guide to do this. Thanks