I was paid a bonus in 2016 and in 2017 I had to payback a prorate of my unearned bonus, gross. I paid taxes on that income, where do I deduct that from my taxable wages?

I received a sign-on bonus in December 2016; I left the Company in October 2017. I had to payback a prorated amount of the sign-on bonus, gross. Since I paid taxes on the amount I paid back, how do I deduct that from my taxable income on my 2017 tax return?