Where do I find a letter 6475

The IRS mails it to you.   Or do you need to enter it?

Yes you need to enter it to see if you got the right amount or qualify for more.  Only enter the 3rd Stimulus payment(that was 1400 per person).  And you should have letter 6475 from the IRS saying how much they sent you.  If you are married you should each get a letter for half.

To get to the stimulus questions in TurboTax at any time, you can search for stimulus or recovery rebate credit then hit ENTER and there should be a Jump to link

If you are trying to trigger it,

Click on Other Tax Situations at top

Click on Let's get started

Answer some questions then Continue

Then click on Let's keep going

Next screen is for the Third Stimulus, if you qualify

If you did not get prompted to enter your stimulus information, that means you either:

1. Filed as a dependent being claimed on another tax return, or 
2. have an AGI too high to claim the recovery rebate