Line 32600 is the sum of amounts that your spouse/partner doesn't need to use on their return to reduce their federal tax payable to zero that can be transferred to you.
If you're preparing your spouse/partner's return together with your own in TurboTax, TurboTax automtically transfers eligible amounts between you.
If you're not preparing your returns together, TurboTax calcualtes any eligible transfer amounts for you based on the info you entered for your spouse in the Setting Up/Introduction section of your TurboTax return.