If you filed your return without including all of your deductions or donations for 2017, then you can amend your return to include the ones that were left off. They must be filed with your 2017 return and cannot be included with your 2018 return.
See the following TurboTax article for information about how to amend your 2017 tax return. Be sure to click the blue link for whether you used TurboTax online or TurboTax CD/downloaded version for your return.
https://ttlc.intuit.com/replies/6603004
