Per IRS Instructions for Form 8962, Premium Tax Credit, page 6:

Note. If an individual in your tax family was enrolled in a policy with an individual in another tax family and you are not taking the PTC, the taxpayer who is claiming the individual not in your tax family may agree to reconcile all APTC paid for the policy.

For more information, refer to the examples in the instructions for Form 8962.

To enter shared allocation:

1. From within your TaxAct return (Online or Desktop), click Federal (on smaller devices, click in the top left corner of your screen, then click Federal).
2. Click the Health Insurance dropdown, then click Premium tax credit.
3. Click + Add Form 1095-A to create a new copy of the form or click Edit to edit a form already created (desktop program: click Review instead of Edit).
4. On the screen titled Health Insurance - PTC - Allocation of Policy Amounts, select Yes.
5. Continue with the interview process to enter your information.

Note that any link in the information above is updated each year automatically and will take you to the most recent version of the webpage or document at the time it is accessed.