Are you stating that (a) there really was no rollover (distribution)? and (b) there is no change in the tax return?

There is no requirement to file an amended return. https://www.irs.gov/taxtopics/tc308

"If you discover an error after filing your return, you may need to amend your return. The IRS may correct mathematical, clerical errors on a return and may accept returns without certain required forms or schedules. In these instances, there's no need to amend your return. However, do file an amended return if there's a change in your filing status, income, deductions, credits or tax liability." 

I would consider preparing a note to attach to the client copy of the tax return.