Step 1, Go to Form 1095-A and subtract Col C from Col A
Step 2, Go to Form 8962 Premium Tax Credit, You should have an amount either on Line 26 (if you are owed an additional PTC) or line 29 (if your advanced PTC was too large)
If you have an amount on line 26, it shows up in Schedule 3 Additional Credits, or if you have an amount on Line 29, it shows up in Schedule 2 Additional Taxes
In my case I had an amount on Line 26 and if I subtract that amount from the amount in Step 1, I get the amount that TT has for Line 2b - it was off by $1 but I'm assuming it's round off somewhere in the calculations.
I'm guessing if there is a value on Line 29 instead, it would still be subtracted from the Step 1 amount since either way it ends up as a tax credit or additional taxes.
Hope this helps.
