Find an item that is set to send offers automatically (you can display them all with this link: https://www.ebay.com/sh/lst/active?catType=storeCategories&status=SIO_AUTO_SEND_ENABLED&q_field1=tit... )
Click "Manage Offers" on the left if it's visible, or from the dropdown menu to the left of the item name if it's not the default visible link.
In the Manage Offers page, click "Change Offer Settings"

If you have offers sending automatically, there will be an option there to turn it off (we don't have any currently, so I don't have a screenshot of that page).