Hi Aadhik, 

I think this might be what you're looking for: https://caulibeam.outsystemscloud.com/DropdownSearch/.

Am pretty new to reactive web so there might be a much better way to do this.

Here are the thing's i've done:

1. Set an onready function for your screen to call a javascript once the screen is loaded

2. In the javascript called, I'm passing in the element id of the dropdowntag and binding the search event to the listener. I've implemented a timer logic here so that it allows user time to complete typing before triggering the event to create new item. 

To get the value entered, i retrieved it from the input of that control by getting the element for class "choices__input choices__input--cloned" (there might be a better way to do this). 

Lastly i call the client action to add a new name and pass in the value

3. Finally, the client logic implements the actions to store a new value in the entity, refresh the data and append the new item into the selected item list. 

Hope this helps :)