In order to carryback excess foreign tax credits from 2019 to 2018, which form(s) should I file with IRS other than 1040 X?

Yes, you need to submit the 1040X, the form 1040 and form 1116.  

Once you have entered the changes into the TurboTax program, when you print it out, chose the option to print All Official Forms Required for Filing.  The program prints out the forms you need to submit, along with instructions on where to mail the forms.

Remember to sign and date your forms before you mail them in.