How to update users in watchlist on standard ticket page on service portal?

[Utkarsha]

Hi Experts, 

I am newbie to the custom widget creation..... I am working on watchlist widget to add users in watchlist for respective incident record 

The issue is whenever I am clicking on update button nothing is happening 

I want button should update users in watchlist for incident records

Could anyone please guide what exactly wrong with the code here? 

Thank you in advance.