You are eligible for 4 years in total, but also only for the first 4 years of full-time undergraduate study (the first 4 years of a traditional college schedule). So if you were a student starting in 2021, you claim the credit on your tax returns for 2021, 2022, 2023, and 2024.
However, the credit is only available if you are not claimed as a dependent by anyone else, and only if you have enough income to owe taxes. The credit is not free money and can't be refunded to you if you don't owe taxes. (A portion of the credit can be paid even if you have no income, but only if you are over age 23 or you are younger than 23 but both parents are deceased.) If you are a dependent of your parents, they probably claimed the credit on your behalf since they would be legally entitled to it.
You can prepare an original 2021 return to see if you qualify (or an amended return if you already filed) but you may need to pay for Turbotax for the 2021 year in order to calculate if you are actually eligible. There is a 60 day money back guarantee if you buy the program and don;t use it because you don;t qualify, but you still have to buy the program up front to see if you qualify.
