How do I make an adjustment to income for the $300 above the line charitable contribution provided for in the CARES act?

That might be on your 2020 return you file next year.  Not for 2019.

I have entered greater 300 dollars in the cc part of TT but initially had entered 100- now only the 100 shows up on the F 1040 and more disturbingly your screen on income does not not adjustment to income for editing?

I don't understand your question.  If you take the Standard Deduction you can also deduct up to $300 Charity on 1040 line 10b.  Go though the deduction section and enter your charity amounts.  Then keep going and finish that section.  It should say the Standard Deduction is right for you.  Then it will add the amount to line 10b.