The Form 8962, Premium Tax Credit has not yet been finalized so that is why you are not seeing the change when adding income on your tax return. The TurboTax program will have several updates before it can be used to file a 2018 tax return.
You can see which forms and schedules have not been finalized for your tax return in the Federal Review section of the desktop program.
Also, use this TurboTax support FAQ for the federal forms availability - https://ttlc.intuit.com/questions/1908854-irs-forms-availability-table-for-turbotax-individual-perso...
