When it ask do I want to use my earned income for 2019 on my return, where do i find that information at on my 1040 form from 2019

Generally, earned income includes wages (including non-taxable combat pay), tips, and other payments received for services you personally performed.

This usually includes the total of the amounts reported on:

 - Form 1040, line 7 (Wages, salaries and tips)
 - Schedule C, 1040 line 12 (net business income)
 - Schedule F, 1040 line 18 (net farm income) 

My 2019 1040 has line 7a and 7b, but the number is same. So which number is I need?

Make sure you are looking at your 1040.  Line 7 does not have an a and b.

Yes -- yes it does have a line 7a and 7b  7a is "Other income from Schedule 1, Line 9" Line 7b has "Add Lines 1,2b,3b,4b,5b,6 and 7a. This is your total income."