1) Select the Asset/Folder you want to hide/show
2) Select Properties -> Access
3) If the asset/folder current gets it's access rights from a parent, you will need to uncheck that box
4) You will see a option called view, click on it
5) You will see another column called row, all checked groups can see the folder/asset
6) Find the row containing the group you want to change, check them if you want them to see the folder/asset uncheck to hide
7) Save you changes