I have a carry forward loss from a company that is now a C-corp. How do I include their loss from last year on this year's tax return (form 8995, line 3)?

What are you talking about ?   Did you change from an S-Corp to a C-Corp ?  

Under Regs. Sec. 1. 199A - 1 (d) (2) (iii) (B), the negative overall QBI amount carries forward to the succeeding year and is treated as arising from a separate trade or business. Those losses carry over indefinitely until completely offset by positive QBI. A C-corp does not have QBI. so that loss can't be used until you have QBI from another souce. 

I do have K1s from other companies.  My question related to how I enter last year's carry forward loss into TurboTax.  This is my first year using TurboTax, so still finding my way around. 

I spoke over the phone with a support person at TurboTax.  They were very helpful and it turns out it doesn't matter that I no longer receive a K1 from the company that generated the original loss (they converted from an S-corp to a C-corp). 

Last year's carry loss forward is entered as follows:   

• Click on Wages and Income -> Other Business situations -> Net Operating Loss/QBI Carryforward Loss
• Leave Net Operating Loss for prior year blank
• Under Qualified Business Income Loss Carryovers
• Enter the value from last year’s Form 8995, line 16