Try
I_FIELD-FLDNAME = 'F0001'.
I_FIELD-DYFLDNAME = 'WA_SCHEDULE-EBELN'.
APPEND I_FIELD.
CLEAR I_FIELD.
I_FIELD-FLDNAME = 'F0002'.
I_FIELD-DYFLDNAME = 'WA_SCHEDULE-EBELP'.
APPEND I_FIELD.
CLEAR I_FIELD.
0001 in F0001 relates to your first field in IT_PO table