As noted by @Bsch4477 the key is did he earn more than $4300 in 2021? If not you can claim him and both you and him will need to file amendments. You should wait for both of your original returns to be processed by the IRS (refunds deposited).
He will adjust his return to show that he can be claimed by someone else (checking the box in the "My Info" section). You will then amend to show him as a dependent on your returns. He will probably not owe any taxes but you will be due a refund.
In TurboTax just sign in and select the "Amend" option and follow the prompts.
Here is Publication 501 for reference. See table 5 for the dependent qualifications.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
