In 2018 did you request an extension to file your 2017 return? If you did not do that, then you have already forfeited the refund you are seeing on the 2017 form, and that refund will not be applied to your 2018 tax.
If you did get an extension, you are okay until October 15, 2021.
https://turbotax.intuit.com/tax-tips/tax-refund/last-chance-to-claim-your-tax-refund/L1ySMyA2H
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