Im pretty sure my former employer made a mistake on my w2 so im trying to file an extension what form do I need for that situation

Here, you can file an extension for 2024: Free Federal Extension. Note this is an extension of time to file, not an extension of time to pay.

I'd recommend taking a look at your last paystub from 2024 and comparing the withholding to your W-2.  If you find a discrepancy, you'll need to work with your employer to get a corrected W-2.

Remember that an extension does not give you more time to pay.   You need to pay your tax due by April 15.   The extension only gives you more time to prepare and file your tax return forms.

https://turbotax.intuit.com/irs-tax-extensions/

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-extension/need-file-extension-personal-state-taxes/L32Mt8ZNv_US_en_US?uid=m9a3q808

You will need to ask your employer about the federal withholding amount in box 2.   Did you give them a W-4?  Maybe you did not ask for enough to be withheld?   Or...depending on your filing status and on whether you have dependents, perhaps they only needed to withhold a small amount.   If, for instance, your filing status is Head of Household, they would not have withheld much for the amount you earned.

W-4

https://turbotax.intuit.com/tax-tools/calculators/w4/ 

https://www.irs.gov/individuals/tax-withholding-estimator

https://www.irs.gov/pub/irs-pdf/fw4.pdf