Customize combobox of templating variables screen to listbox

Normally, templating variables screen show as combobox (as picture).
But I want to change from combobox to listbox. And when I click a item in listbox (a server), metrics of this server show in dashboard.
I think modify source code and rebuild it.
Please guide me to change it.

Can you answer my question, please?

Just check the multi value option in your template variable options.


Will make the dropdown into a combo box (with checkboxes so you can select multiple values)

Oh, sorry.
I want to chose just a variable.
It same as listbox.

? not sure I understand