How do I file a 1040 or 1040SR to claim the credit for not getting my stimulus check?

[MinhT1]

If you did not receive your first and/or second stimulus payment or if the amount received is not correct, you can claim it on your 2020 tax return as the Recovery Rebate Credit.

In TurboTax Online, to claim the Recovery Rebate credit please do the following:

1. Sign into your account and continue from where you left off
2. Click on Federal in the left-hand column, then on Federal Review on the top of the screen
3. On the next page titled Let's make sure you got the right stimulus amount, click on Continue
4. Follow the interview
5. TurboTax will determine whether you are entitled to any additional stimulus
6. Any stimulus amount remaining due to you will show as a credit on line 30 of your form 1040 or 1040-SR.

[SteamTrain]

....thing is...if it's being sent by mail, you may not know for sure you aren't getting one for another full week...so you still need to wait for at least another week.

[VolvoGirl]

And there's no hurry to file.  The IRS won't open Efiling until Jan 27, 2021 or later.  Turbo Tax will let you file now but they will hold all the returns until the IRS opens.

[Opus 17]

If you have no other taxable income, you will have to create $1 of fake income to be able to e-file.  You can call it hobby income or bank interest.

If you will be filing a tax return this year, you must not file a special return to claim the rebate faster.  You only file one tax return when you have all your documents and all your tax situations are resolved.  Filing first to get the rebate, then filing an amended return later, will delay the rest of your refund by 6 months or longer.