What should I have to do if I live in the U.S. for 2 months and a half only?

If you're required to file a federal return for 2023, you can use Form 1040 (US Individual Income Tax Return) if any of these are true:

• You're a US citizen.
• You're a resident of the US or Puerto Rico.
• You have a Permanent Resident Card ("green card").
• You're a nonresident alien married to a US citizen/resident alien, with whom you'll file a joint return.
• You meet the substantial presence test, which means you were physically present in the US for at least 31 days in 2023 and at least 183 days in 2021 through 2023, according to this formula:

2023 days + (2022 days)/3 + (2021 days)/6 >= 183   For Example, see 1040 or 1040-NR

Unlike the 1040, there's no minimum income threshold for filing a 1040-NR. In other words, nonresident aliens with US income, regardless of amount, are required to file a 1040-NR.