Accrual basis taxpayers report their income when they perform services, regardless of when they receive their payment or compensation for their services.
Since you've reported the income in 2017 but the 1099 says 2018, report it, then show the IRS that you've backed it out. An example:
2018 Income: $50,000 (including 1099's of $10,000 reported in 2017)
2017 1099's -$10,000
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2018 Net Income: $40,000
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