Usually, a distribution from a qualified retirement plan is treated as ordinary income in the year in which it is received. However, for someone born before 1936, there is a special 10-year averaging rule. It only applies, however, to a lump-sum distribution. This is a distribution payable within a single tax year of a plan participant’s entire balance from all of the employer’s qualified plans of one kind (for example, pension, profit-sharing, or stock bonus plans).
On Form 1040X, you may file an amended return within a three-year period to claim a refund or correct a mistake made on an original or previously amended return.