Accidents happen, and that's what the UNDO button is for.
If at any point during your draft you need to UNDO a pick (or several picks in a row), you can access the "Undo last pick" tool from the (...) drop-down:
Important notes:
- Only the Commissioner will have access to this tool, and only while in "Commish Mode"
- For Auction style drafts, the Commissioner will only have access to this tool during the "Nomination" process (it is not available while live bidding is taking place).