Adjust jquery plugin for selection

Hi, I used chosen jquery plugin for selecting multiple items on a page, now I want to allow custom items in it from the user that are not included by default in select box.

Please I will not share ftp details. You have to write the script and share and I will put it on live site where you ask me to.

What I want is that the custom skill is allowed in selection.
https://imghostr .com/b39b7e_d8a

Live page where I want the edit.
https://www.jobguru .pk/add-job

Adjust links so they work for you.

Thanks