If you believe it is referring to the annualized income to reduce any penalty for underpayment, the Form 2210 is scheduled to be available on February 11th.  Use this link to continue to check the availability - When will federal forms be available

If you are referring to your state return you can check the availability of those forms here. 

You can visit the Schedule SE section in TurboTax by:

1. Open (continue) your return if it isn’t already open.
2. Inside TurboTax, search for sch SE and then select the Jump to link in the search results.
3. On the Self-Employment Tax screen, select Make Adjustments.

I was having the same issue...only difference is that I'm using the desktop version, not online.

In the questionnaire, it asked if I wanted to defer my SE tax payment until 2021, I clicked Yes to find out more info, but went back and answered No as I decided to just pay it now since I'm receiving a refund.

In the error check, it returned a result of Sch SE-T: max deferral line 18 must be entered (which is the net profit between 3/27 and 12/31 as shown on Sch C line 3...I had to go directly to form Sch SE-T to find this info). I went back to the questionnaire and selected No again for deferment, but the error was still there. So, I figured out that amount to see what would happen, and obviously it deferred a percentage of my payment until next year...which I did not want to do. 

After talking with a TT Rep, we concluded the fix was to put in $0 as that amount (either in the questionnaire or directly in the form), which then returned no errors during review. Even though that is not the correct value, it was the only way to override the error and to not defer a portion of my payment. I'm assuming the IRS won't care as they are getting my full SE tax payment now.

I feel this is somewhat of a bug in that choosing No in the questionnaire doesn't override a previous selection of Yes (should you go back to the question) or that the error check doesn't full explain what you are doing by inputting this amount, and give you an option to not defer payment so as to fix the error. 

It seems like you should be able to go directly to the Sch SE-T form for the online version at anytime to change the line 18 amount, but I'm not familiar with that interface. If it's not possible given the point you are at, this may not help you, but may help others that come across this post. 

I think the correct way to do it is to leave Line 18 of Schedule SE with the proper amount, but then go to Line 12e of Schedule 3 to make that number $0.

I agree, that seems like a much better way to do it.

Only issue I had with the desktop version is that Line 12e of Schedule 3 is not an editable field. It jumps me over to the 1040/1040SR Wks > Schedule 3 Part II: Other Payments & Refundable Credits > Line 12e.

You can not edit this field either, but if you go up to Line 11 in the Deferral for Certain Schedule H or SE Filers Smart Worksheet, it allows you to put in the amount you want to defer up to the maximum amount on Line 10. If you put in $0, it will make Line 12e of Part II amount blank as well as Line 12e of Schedule 3 for Other Payments and Refundable Credits as they are linked.

This solves...

1) the error from Sch SE-T

2) it allows you to put in the correct amount of your income from 3.27-12.31 on Sch SE-T Line 18

3) eliminates deferral of SE tax payment

Thanks @AmeliesUncle! Not sure if that helps out @jnlkepner as well.