if there was an AMT tax carryforward it should have shown on form 8801 on line 26 (2020 vers of 8801) the form would have been generated each year there was an AMT tax credit carryforward. however, if you did not claim the amt credit properly on prior returns, it's too late to amend them so the credit would be lost. you don't get to pick the year to use the c/f. 2013 is carried to 2014 and if any is left carries to 2015 and so on.
