Form 5330 - Notice CP-220

A client filed a 5330 to pay an excise tax for unpaid minimum contributions.  The client received a Notice CP-220 that assesses an adjustment to the excise tax.  We have no idea how the IRS got its numbers, and we want to appeal.  There is nothing on the face of the notice that explains how to appeal.  Does anybody know how?  Do we just write back to the address on the notice and say we want to appeal?