If something has ended up on dpaste that shouldn't be there, you have three options for taking care of it:
Option 1: Do it yourself: If you created the item while logged in, there will be a "Delete" button in the button bar. (If you're not a registered user yet, you can sign up here, via GitHub/GitLab etc. if you like.)
Option 2: Wait it out: Above the item's button bar the number of days until item expiration is shown; when this time limit is reached, it will be deleted automatically.
Option 3: Special request: If you have a special case, submit a support ticket requesting deletion and explaining the reason (e.g. leaked secrets or TOS violation).
If you are concerned about others seeing something you have accidentally posted: Unless you checked the "Public" option for that item, it won't be listed anywhere on the site.