Per Instructions for Form 8962, Premium Tax Credit (PTC), on page 10:
Allocating policy amounts. You need to allocate policy amounts (enrollment premiums, SLCSP premiums, and/or APTC) on a Form 1095-A between your tax family and another tax family if:
For example, if you could have claimed your child as a dependent, but chose not to, follow the instructions below to report their health insurance on your return.
To report your child's health insurance:
If you could not claim the child as a dependent, the child should enter the information on his or her own return (you must provide a copy of the Form 1095-A you received in this case).
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.