My Grayscale Bitcoin Trust BTC transaction are being reported on TurboTax as having a cost of $0.00. What "type of investment" should I select for the edit of the cost?

Because Grayscale Bitcoin Trust has referred to itself as a fund, you can select the option for Mutual fund, index fund, or ETF.  The type of investment should not matter as much as the cost basis you are trying to edit.  

@R-C-B