You can't. If your child was born in 2020 you cannot add him to a 2019 tax return. When you prepare your 2020 tax return in 2021--next year-- you can claim your child on that tax return. The stimulus checks that people have received this year are really an advance for a credit you will be able to get on your tax return next year. But congrats on your new little boy!
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
