Any contribution amounts in box 12 of the W-2, and with a Code "D" or "AA" (those are your TSP and ROTH TSP contributions) will automatically be considered for the "Retirement Savings Contribution Credit" (RSCC).
But, after you've entered ALL your income, you do have to go thru the RSCC section on the "Deductions&Credits" page to see if you qualify.
There are AGI limits that can disqualify you from that credit, but TTX will kick you out of it if you don't qualify because of that. Also some other disqualifications , but the RSCC interview questions cover those