Turbotax is asking me to fill out line 18 of the Maximum Deferral of Self-Employment Tax Payments section. I don't know what to enter.

I had a 1099NEC for 2020 for the amount of $2,100 working as a tester. I am low income and make about 20,000 a year. I am not sure what to add to line 18 "Enter the portion of line 3" Which line 3? and if I look on previous page line 3 is empty.