Urgent please help. F24-Unmarried Son/Daughter of Permanent Resident

Hello everyone, I am new here and will like to apologise if I am posting in the wrong forum.

Please I need answers to two very urgent questions regarding my interview.



1) My father filed for me as "F24-Unmarried Son/Daughter of Permanent Resident" and I have been scheduled for interview in London UK but I can't make the date of the interview because I will be away from the country for training that has already been paid for and not refundable.

My question is will I be able to reschedule the interview? If yes how do I go about it and will it have a negative impact on my application/interview?



2) I have a 3 years old son which I stated on the form and I said he will be joining me on a later date in the US when I relocate but I have changed my mind and will like him to relocate with me at the same time.

My question here is how can I add my son at this stage and what documents will be required? Also will I have custody issues relocating with my son without his mum(my partner)?



Please I will be super grateful if I get a comprehensive response asap. 

Many thanks

Please can someone with knowledge of this kindly advice?