The same way you claim a dependent who is under 18. In My Info you enter the information about the dependent including the Social Security number. For a dependent over the age of 16, you will get the credit for other dependents. You will not get stimulus money. And the person who you claimed will not get stimulus money, since dependents are not eligible to get a stimulus check.
CREDIT FOR OTHER DEPENDENTS
https://ttlc.intuit.com/questions/4499708-what-is-the-500-credit-for-other-dependents-family-tax-credit