There is no place to enter anything about stimulus checks on a 2023 tax return. The stimulus checks were issued for tax years 2020 and 2021. If your son could be claimed as a dependent for 2020 or 2021 he was not eligible for a stimulus check and would not be eligible now for the credit even if he files a late return for 2020 or 2021.
How old was he in 2020? Could he be claimed as someone else's dependent? Same question for 2021.