Create Dynamic Dependent dropdown

Hi

I have followed this post: https://suitecrm.com/forum/developer-help/260-dynamic-dropdown-inside-studio

I wanted to create dropdowns in such a way that when the user selects the city, the corresponding Region is automatically filled

For example, if I select Shanghai in the city column, I want it to be populated with the option Asia.

I Tried but the city column is showing blank

Can anyone help me out? Thanks in advance