Fed review says Sch SE-T max deferral line 18 is too large. I changed it to zero - still says "too large"! (How can that be?) Cant find place to amend or fix. HELP!

If you do not want to defer then remove the zero and leave line 18 blank.  Review and see if the error disappears.

If there is still a problem then follow there steps:

 delete Sch SE-T, take a quick run through of the self-employment to recalculate Sch SE-T, and then turn off the Max Deferral. 

To do this in TurboTax, follow these steps: 

First, delete Sch SE-T that applies by following these steps: 

1. From the left menu, select Tax Tools. 

2. Select Tools. 

3. Scroll to Delete a Form. 

4. Scroll to Sch SE-T, select Delete, confirm the deletion. 

Next, to replace Sch SE-T, return to the self-employment income & expenses interview in the Income & Expenses section and select Edit/Add. 

1. Select Edit for your business. 

2. Scroll down to Done so that the Sch SE is recalculated.  

3. Finish any other questions in the self-employment interview and click Continue.  

Lastly, revisit the section for the Self-employment tax deferral entry: 

1. Return to the Deductions & Credits section. 

2. Scroll to Tax relief related to COVID-19 and Show More. 

3. Select Self-employment tax deferral and select Revisit. 

4. Answer Yes at the next screen to get back to Let's start by getting your eligible income. 

   1. If you do not want to defer any self-employment income, "Enter your eligible self-employment income" should be blank. 

      1. Select Continue. 

   2. At Tell us how much you'd like to defer, "Enter amount" should be blank. 

      1. Select Continue. 

5. Scroll down and select Wrap up Tax Breaks and Continue. 

6. Run through the Federal Review again. 

IRS Defer Self Employment Tax