If you are talking about this widget Mendix Marketplace - Custom Dropdown then you download this widget code from here mendixlabs/CustomDropdown: A custom dropdown selection widget for Mendix. This widget allows you to fully customize the behaviour of the dropdown widget from within Mendix. Microflows can be set to determine exactly what should happen on select/create/clear actions. (github.com).
Then you can modify code according to you.
Please accept answer if this helps you.