You posted this in another area as well. But you have not identified what you want the csv to do. Csv uploads can do a lot. But if you are looking to add people to sessions in f2f, it seems unlikely you will be successful. I consulted with someone who has substantially more tech-brain than me (which is not saying much, but he is very competent) and he had come to the conclusion the while you might be able to add sessions by csv, it would be substantially more time and effort than it would ever be worth to try to add people to sessions that way and it is possible it would not work at all. The table structure for f2f is very complex, making something like this even more so.
Make your participants sign themselves up. Give them a deadline.