How to fixed the combobox value after selectedindex cange

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C#

ASP.NET

In the windows form application i am taking two combobox. 1st combobox bind data from data base.now when a value is selected from 1st combobox with this selected value is reflected to 2nd selected box.
means
1st combobox name--CenterName
--Select--
Deorali
Gangtok
Namchi

2nd combobox name--District


when i select CenterName(Deorali)then District(East) is come with the help of SelectedIndexChange and with the some information i save it.

but after save it. i see that i the 1st combobox --Select-- item is come for then i again select CenterName(Deorali).which i dont.

so i want to know how to fixed that value (Deorali) after save.
CenterName never change when i want then change.