Yes, if he is claimed as a dependent on your return, you will need to enter his 1095-A on your return. His Premium Tax Credit is then based on your income plus his.
How long ago did you file? The IRS should catch this error, but once in a while they dont
Ok, so the IRS will likely send you a letter telling you, you need to fill out form 8962. To do that in TurboTax you will just log back into your return by clicking add a state, then you will click on the Health Insurance section walk through and say Yes, I had one of these types of coverage. Then enter the 1095-A. However, do not do this until you get the letter from them. If they miss it and process your refund, you will need to amend. So wait until your return is fully processed before doing anything. It is MUCH slower this year so it may take a bit longer than normal due to the gov shut down.