I just found out that I can claim private extended health benefits monthly premiums. Can I claim the previous years that I missed? I’ve been paying for last 3 yrs.

You would have to go back and adjust your returns to add the premiums. Even then, the premiums would be treated the same as medical expenses, so you could claim the total of the eligible expenses minus the lesser of the following amounts:

• $2,759 (in 2024, it will be different each year) OR
• 3% of your net income (line 23600 of your tax return)

So, you may not get the credit if the amount is too low.

 

This TurboTax FAQ tells you how you can adjust your filed return using ReFile: I've filed my tax return. Can I still make changes?