In 2018 I claimed a business loss on schedule C. 1. Can I pay back the loss in 2019? 2. Would this be considered an operating expense (which would reduce the profit)?

[VolvoGirl]

Pay back?  A Net Loss on Schedule C is income - expenses.  You get to deduct the net loss from your other income so you got the benefit of it.  You can't use it in 2019.  You can't shift it to the next year.  

[pk]

NOL ( Net Operating Loss) can be carried back one year and carried forward .  That is the amount of loss  more than the allowed $3000 for the current year can be carried back first  and then carried forward.   Once TurboTax recognizes  that you have  recognized the allowable NOL, the rest would be suspended ( you get to choose if you want to go back or just go forward ) and will be shown on federal carryover worksheet.  So not to worry