Hi,
The username who created the reservation is in field RKPF-USNAM.
In standard DBM this field is not filled during execution of action RESERV_UPDATE
when DBM order is saved and reservation is created.
Therefore in MB24 you cannot select reservations with selection of User name.
You can try to create customer BADI implementation of BADI /DBM/BADI_OE_ACTION_EXECUTE which should be executed after DBM standard implementation /DBM/ORD_AX_RESERV_UPDATE.
Find details in configuration book of order engine.
The username is pouplated e.g. in MS_VBAK_COM-ERNAM of object DBM-order.
So, if reservation is created with standard implementation you can try to change RKPF-USNAM with the user who is creating the DBM-order.
Hope this helps.
Regards
Joachim