If you purchased your theme directly from the Out of the Sandbox website:
You'll need to request a fresh theme file from our Merchant Success Team.
Please include a copy or screenshot image of the original purchase receipt within the request so we can confirm and get you your fresh copy faster!
Note: If you happen to still have your original order confirmation email containing the download link, you can also use that to download a default theme file.
If you purchased your theme from the Shopify Theme Store:
If you bought the theme through the Shopify, then you can also visit the Themes Store while logged into your Shopify account (must be logged into the same shop that you originally purchased the theme), locate your theme, and click on Add latest version.
The blank theme will be added to the Themes page of your Shopify admin.