How to update watchlist users on standard ticket page on sp?

[Utkarsha]

Hello Experts,

I have been trying to add users in watchlist for standard ticket tab on service portal 

I created watchlist custom widget for that 

The issue is whenever I am trying to click on update,  user updation is not happening 

Could anyone please guide me where exactly I need to make changes in my code so that it will update the selected users in watchlist for respective incident record? 

Thank you in advance! 

Please find the attached widget code for the same.