Part II, and everyone must complete Part III. If you are not able to file your business income tax return by the original due date, you can request a tax extension by mailing Form 7004 to the appropriate address (see Instructions for IRS Form 7004) or you can e-file Form 7004 online.f you chose to e-file Tax Form 7004 through the FileLater system and your request is rejected for any reason, you may make corrections and resubmit your tax extension at no extra charge.