Hi Hafizul,
Follow this step It workout form me..
1) choose BNKSA field from Service fields for PA.
In input help choose 0001-bnksa as value help
2) Set field Attributes like below image
3) Go to form layout choose attributes for the field and give display type as below. Dropdown will return description but Input field will return Value of bank type
4) out put will be
Sure this will work out...
Regards,
Arun