2. How to swap
Think about how you want to swap. There are several ways to go about it, depending on the size of the group. Some examples of how you can do it:
All garments are checked one by one and tried on by everyone who is interested. Together you decide who gets the item. You could even set up some sort of lottery system to determine who gets an item when multiple people are interested. Make sure you divide the items fairly.
All clothes are hung/laid down, everyone can choose what he/she likes. If needed you can work with stickers or tokens: with stickers you can let everyone indicate what they are interested in, with tokens you can determine how many pieces someone can take with them based on what he / she has brought.