By default, the Checkout page is inaccessible and only some very basic information can be altered for security reasons (such as changing the text that is already visible on the page). Due to Shopify limitations, changes on the Checkout page are possible only for Shopify Plus accounts. You can check more details about the Shopify Plus plan on the link here.
Please note that Carson is not able to guarantee the possibility of making changes to your Checkout page. However, if you have Shopify Plus, please contact us with the details of the changes you would need and we would check if we can assist you.