How do I deduct mileage for a Misc. Income when I don't receive a form 1099? I put the income into Misc. Income under "Less Common Income".

I get paid for blood plasma donations, which I do not receive a 1099.  Researching it through TurboTax, it says to enter those payments (made to a prepaid debit card) as Miscellaneous Income under the "Less Common Income" section.  Where do I go to deduct mileage related to the blood plasma donation income?