Note, the Kohl's Cash expiration date is 11/05//2017.
Log in to your Discover Account
Go to the Rewards Tab
Click on "Discover Deals"
Enter Kohl's in the search field (Do not choose "Kohl's online", choose "Kohl's")
Find the $10 off $30 offer and click "View Deal" (availability may vary)
Note the barcode
Go to Kohl's.com
Add merchandise to cart
Proceed to checkout
Click on the "Kohl's Cash and Promos" field to enter the barcode and 4-digit pin for $10 off (will apply to your total as Kohl's Cash)