How to reset parameter value

Hi,
I have a created a parameter(List box) in report using vrm_set_values i have assigned data to it.
Data format ex:
1. key: ab_12

text: Testing1
2.Key: ab_13
Text: Testing2
So according to above data, Testing1 and Testing2 are desplaying in list box.
case: when i select any value(eg:Testing2 ) in list box and press F8. report is executing in a right way.
After execution, list box is showing selected value's key (ab_13). this is not user friendly.
Dropdown should not show key value.
Pls help me on this.