No need to amend 2019 for this. It can be reconciled on his 2020 return.
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
This will be found in the Federal Review section under Other Tax Situations. If you are eligible.It will end up on line 30 of your 2020 Form 1040.
https://www.irs.gov/newsroom/economic-impact-payment-information-center-topic-j-reconciling-on-your-...
https://www.irs.gov/coronavirus/coronavirus-tax-relief-and-economic-impact-payments-for-individuals-...
https://ttlc.intuit.com/community/tax-topics/help/how-will-the-stimulus-package-impact-me/00/1393859
good post with screen shots for recovery rebate credit
https://ttlc.intuit.com/community/taxes/discussion/filed-as-an-independent-and-single-but-haven-t-re...
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