You need legal advice. Generally speaking, the IRS can't audit you or assess penalties more than 3 years after you file (sometimes, 6 years is allowed). So generally, they can't be assessing you for 2016-2018 at this point, unless they assessed you a long time ago and you are just now trying to clean it up; or if you never filed for those years (which means the 3 and 6 year clocks never started). I suspect there are a number of facts you have left out of your question. You probably need in person help from a tax professional you hire and can work with directly.
