How should I claim interest income from the IRS?

it is reported just like any other interest.  You will need to enter it yourself as IRS for payer and then the amount of the interest.

Form 1099-INT reports interest from banks, brokerages, and other financial institutions. Here's how to enter a 1099-INT:

1. Sign in to your TurboTax account and open or continue your return.
2. Select Federal from the menu, then Wages & Income.
3. Locate the section titled Investments & Savings and select Show More, then select Start or Revisit next to Interest on 1099-INT.
4. Select Yes on the screen Did you receive any investment income? then Continue.
   • If you see the screen Your investments & savings or Here's your 1099-INT info, select Add investments or Add another 1099-INT, then Continue.
5. On the next screen, select how you want to enter your Form 1099-INT:
   • If you want to import your form, search for your brokerage or financial institution. Sign in to your online account and select Get my form.
   • If you want to upload a copy of your form or manually enter the info, select Enter a different way, and follow the instructions to enter your 1099-INT.
6. On the screen Do any of these uncommon situations apply? check the boxes according to your situation and Continue.

Enter interest income in the Search box locate in the upper right of the program screen. Click on Jump to interest income

On the screen Did you receive any interest income? Click on Yes

On the next screen click on Continue

On the screen Let's import your tax info Click on Change how I enter my form

On the screen How do you want to add your 1099‑INT? Click on Type it in myself

Enter IRS for the name of the payer and enter the amount of interest received in box 1 of the 1099-INT