how to add icon button and click event in formly form for material UI?

I have a select field which contains file name, i want a eye button above select field on right. I am using formly form and UI is angular material. how can i add eye button on right side above select option?

          key:name,
          type:'select',
          defaultValue:'',
          templateOptions:{
              label:label_name,
              placeholder:name,
              required:true,
              options:['abc.txt','cde.txt'],
            }