No one can make you sign anything. It is you obligation to pay attention to what you sign.
All you need to do is File a Form 1040X Amended tax return to included all your expenses. Or contact IRS at the phone number listed on your letter to discuss your account.
The tax preparer only filed you tax return with the tax information you provided him.
You can file a lawsuit against anyone you want, just have proper proof that you supplied the preparer all the documentation you needed to file an accurate return. Then have proof of him making you sign the audit. (Pictures of the Gun to your head)
You have a Tax LIEN on your home because you ignored IRS.
good luck
big mistake
you should have discussed the audit with him before signing anything
find someone else to see if you can challenge