This is a premium feature available with Astra Pro Addon plugin. To use this Pro feature, you need to have the Astra theme along with the Astra Pro Addon installed on your website.
Read about the module here. Make sure that the Easy Digital Downloads Module is activated from Astra Options.
Before that please verify if you have the Easy Digital Downloads plugin installed and activated.
You can find the settings under Appearance > Customize > Easy Digital Downloads > Checkout Page
Following options are available-
Display Apply Coupon Field: Coupon field will be visible at the top of the checkout page. If you don』t want want to display any system for coupons you can disable it.Distraction Free Checkout: When you enable this option, the menu in the header and the first footer of the website will disappear on the checkout page. The option of Distraction Free Checkout overrides the header and footer settings.Checkout Form Width: Let the form width be default or using the Custom option set the custom width for the form.