How to move/copy customer field from EBAN to PO Purchase order

Hello,

I have added field EVERS (shipping instrictions) to table EBAN (CI_EBAN) This field can be changed in transaction ME52N in Purchase requistion. (sofar so good)
But i have problems with the next step.
If this PR is converted into an PO with trx ME59 this field (EVERS) has to be copied the corresponding EKPO field (EKPO-EVERS)

Does someone know where and what code has to be added to accomplish this.

I will be gratefull.

Thanx in advance

regards