I spoke at a university and received a an honorarium, which reimbursed the flight to travel there. I received 1099-NEC, how do I write off the flight, as it wasnt income?

The honorarium was $1000, and the flight was around $700. I don't know how to classify the 1099-NEC (a hobby? self-employment?), and subsequently how to write-off the $700 flight which ultimately was not part of my income.