What happens if ur old boss barely gives u ur w-2 from ur old job that u quit in august but he barely gave it to u now and u already filed ur taxes what do u do ???

if the IRS has not processed your return -  you received your refund or any balance due has cleared through the payment method selected - do nothing until it is.    The IRS may catch the omission and adjust your return accordingly.   if it does not, after your return is processed you will need to prepare an amended return to include the omitted W-2.