You can amend your 2023 tax return to add them as dependents.
See this TurboTax support FAQ for amending a prior year tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...
An 2023 amended return, Form 1040-X, can only be printed and mailed to the IRS. The IRS will take up to 16 weeks or longer to process an amended tax return.
