I'd either enter 0 for Cost Basis or delete those transactions completely....whatever works and lets you continue with the TurboTax program. Since there are no proceeds, these trades are not relevant to your tax situation.
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***