How to amend form 1099-B to report capital gains/loss because what was reported to the IRS by former employer was $0.00 in box 1e?

If you haven't filed your tax return yet, you do not have to amend it.  However, the process to correct the basis will be the same.

To post investments:

1. Sign into TurboTax
2. There is a Sidebar to the left
3. Under Federal
4. Select Wages & Income
5. In the main body, scroll down to Investments and Savings (1099-B, 1099-INT, 1099-DIV, 1099-K, Crypto) 
6. Depending on what you've already posted, you may see different screens
7. If you've already entered transactions, select the account to change
8. [Edit]
9. Choose the stock (Use the Pencil)
10. Under the Cost or other basis 
11. Choose The cost basis is incorrect or missing on my 1099-B.
12. Make the changes