You can't report the term or basis as unknown on your tax return. That's why there's no way to enter it. The brokerage reports it as unknown because they don't have the information. On your tax return you have to fill in the correct information from your own records. You're not just telling the IRS what the brokerage statement says. You have to show the actual details of the transaction, even if not all of the details are on the brokerage statement.
