You will need to switch your Store App to be in 'Coach Mode'. A coach or admin will need to log in.
From there, the store app functions the same as in 'Kiosk Mode', with the exception of the ability to add discounts.
To apply a discount:
Add a product to cart
Once all products have been added, in the checkout list, click on the individual product you wish to add a discount to.
A pop-up will show, with a drop down menu of all preset discounts. Select the discount. *note, the discount will only apply to the product selected. You must which discount to apply to each product in your cart*
Click on the Cart icon, and select which member to charge.