To apply a current year Capital Loss, you will need to make a "Request for Loss Carryback". To do so using TurboTax Self-Employed Online:

Click on > Deductions > Losses Profile > Request for Loss Carrybacks

Select for whom the losses will be claimed (yourself and/or your spouse, as appropriate) > click Continue until you reach the page Net Capital Loss Carrybacks.

On this page, you will see your Net Capital Loss Available for CarryBack, and you can choose the amounts you wish to have applied to previous years.