If you are claiming a net Premium Tax Credit for 2021 — even if you received an increase in your premium tax credits after reconciling and filing your taxes — you must still include Form 8962.
You may need to file an amended tax return if you already filed your 2021 taxes and reported excess APTC or repaid excess APTC.
Visit IRS.gov for more information on filing your 2021 taxes with excess APTC.