How can I add my Form W-2C to my tax amendment in TurboTax if I've already filed and been accepted? Do I directly edit my W-2 directly, or is there a place to upload?

You cannot upload a W-2c. You have to make the corrections manually to the original values.

Are you sure you have to amend your tax return? What did they change on the W-2c? Will the changes make any difference in your tax or your refund?

You should wait to file an amended return until you get the refund from the original return.