Pledges do not have donor adjustments.  Adjustments in the Pledge module do not work like Gift adjustments and therefore you are limited in what can be changed.  In this instance you will have to remove the old pledge and create a new accurate pledge.

Pledge adjustments can:
  • modify the amount of the pledge
  • add installments
  • change the funds associated with the pledge

In order to change the pledge date or donor idcode associated with the pledge you will need to either adjust the pledge to $0 or write off the pledge and then enter a new pledge with the correct details.