Creating subdecks in anking

I am an incoming M2 about to start my cardio block and I have not been keeping up with anki. I havent created any subdecks before but now since I have a backlog I would liek to create a subdeck for my cardio block cards so I can make sure i am focusing on and finishing those everyday (of course I also plan to finish my others too but yktv). 1. how do i/best way to do this and is it possible to have the retention for my cardio cards be set to 90 and i set my others to 85?