it fixes the issue Html.DropDownList() accepts a SelectList as a parameter which has a SelectedValue property. Specify the selected item when you create the SelectList and pass the SelectList to the Html.DropDownList().
Remove one option from dropdown based on the option selected in the before dropdown list
By : user3320498
Date : March 29 2020, 07:55 AM
help you fix your problem Here is my HTML Code. , Try this jQuery:
Enabling a dropdown list based on a selected option from a secondary dropdown list
By : Diguinho Soares RA
Date : November 16 2020, 11:00 PM
this will help When modifying the disabled state of a dropdown that is using the bootstrap-select plugin, you have to call selectpicker('refresh') on the dropdown afterward to update it per the documentation.