Deductions & credits

yes, it is a tax credit (sort of), but that doesn't mean that when  you calculate your tax return there will be ANOTHER $2400 reduced from your tax return. (which is the kinda way I read into your question)

 

look closely at Line 30 of Form 1040 that is where any ADDITIONAL EIP will be listed for people who didn't get the maximum amount back in the spring and are eligible now.   But if you received $2400 in the spring (2 people, no children) then Line 30 will be zero when you complete your return.