You can claim casualty loss in the tax year it occurs, or in the previous tax year. So, in your case, you can amend your 2018 (or even 2017) return to claim the loss.
Please see the TurboTax blog “Tax Benefits Available for Victims of Natural Disaster” and the articles "What if I have property that was lost or damaged (a casualty loss)?" and "I live in a federally declared disaster area, what does that mean for my taxes?" for guidance.
Additionally, please see the TurboTax Help article "How to amend (change or correct) a return you already filed" for instruction on how to amend your previously-filed tax return.