I had an issue with my 2019 return and couldn't get my stimulus. I was told I could write it "line 30 it will apply to your 2020 return" how would I do that in the app

The stimulus check is an advance on a credit you can receive on your 2020 tax return.  If something went wrong or you did not get the stimulus check in 2020, you can get it when you file your 2020 return in early 2021

The Recovery Rebate Credit will be found in the FEDERAL REVIEW section. ( you should see "Let's make sure you got the right stimulus amount”)  If you are eligible it will end up on line 30 of your 2020 Form 1040.

Make sure that you enter ALL of the stimulus money received for the 1st ad 2nd stimulus for yourself, your spouse and your children.

https://www.irs.gov/newsroom/economic-impact-payment-information-center-topic-j-reconciling-on-your-2020-tax-return

https://ttlc.intuit.com/questions/1901539-how-do-i-preview-my-turbotax-online-return-before-filing

Click on Tax Tools on the left side of the screen. Click on Tools. Click on View Tax Summary. Click on Preview my 1040 on the left side of the scree

If you follow the "step by step" process throughout your 2020 preparation of your taxes (meaning always select "walk me through" versus you jumping ahead), once you allow the system to go through its check of your entries for deductions and credits - you click on Continue - then it will tell you what type of deduction (standard or itemized) it has selected for you and gives you the option to change. Make a change if you want, then click on Continue. This will now bring you back to the "Other Tax Situations" page. Scroll to the bottom and click on "Done with Other" - NOW it will ask you whether or not you received your stimulus payment. Select No, since you've indicated you did not, then it tells you what you'll be receiving as a credit. You'll find it....I hope this helps!