I received a W-2c for my 2020 taxes where it shows the Social Security Tax Withheld was incorrect. How do I report this in TurboTax - change the original W-2 amount?

You don't need to amend for the Social Security tax.  Unless it increased and you have more than 1 employer and together they went over the max.  Or if you claimed excess Social Security and they reduced the ss tax.