Few Questions About Crafting

1. It says you can only get one Chest per champion. If someone else gets an S and I get a Chest while playing a certain champion, do I need to play a different champion to be able to get another Chest? Or am I still eligible on that champion, since it was not me who got the S?

2. Where do you even activate the 7 day rental stuff? I accidentally did the rental on the Ward Skin (thinking that it wasn't actually possible to do anything permanently) and I can't find anywhere to turn the ward skin on.

Thanks to whoever answers.