How do I do a write down for lost revenue due to an event in 2019 ie client cancelled a contract without notice, cost my business $14,000 in lost revenue... How do I record that in quickbooks?

If the $14,000 had not been previously shown as income then there is no write off.  Any actual expenses that were incurred for the event would be deducted the same as for any other event.

Hi brchapman65. As btks stated, if you didn't record the $14,000 of income yet, then no action is needed. However, if the income was accounted for but never actually occurred then you will need to delete the transaction. Here's how:

1. Select Transactions from the left side of the screen
2. Now check off the transactions that are not actual income. 
3. Next, click on Exclude
4. Last, press apply. 

No the income will no longer be accounted for in your books. Let me know if there are any other questions or concerns.