Need to amend 2018 taxes for a second time, not sure how to do it in TT

I amended my TT 2018 return and it was processed (refund) by IRS end of 2019.  Just got a notice that a recent law change would allow an additional credit so I need to amend it again.  The process I used in TT to do the first amendment no longer seems to work.  Are there additional steps I need to do in TT to do a 2nd/additional amendment in TT?