The 1st and 2nd stimulus payments were made in tax year 2020. It is now to late to either file a 2020 return or an amended 2020 tax return for a refund. The 2020 returns had to filed on or before May 17, 2024 for a tax refund.
It sounds strange that you received the 1st stimulus check but not the 2nd one--are you sure you did not get that one?
The second stimulus was sent in late 2020 or early 2021; that one was $600 per adult and $600 for qualified children dependents under the age of 17.
If you did not receive the first or second stimulus check,—Sorry—it is too late. The deadline to file a 2020 tax return and get that credit was May 17, 2024.
Check your own bank account for deposits of the stimulus checks, and check your online account with the IRS to see what the IRS shows they sent to you.
Try checking your online account with the IRS (and if you filed a joint return—check for BOTH of you)
https://www.irs.gov/payments/your-online-account
If you need to trace a payment that the IRS says has been issued to you, mail or fax a completed IRS Form 3911, Taxpayer Statement Regarding Refund.