How to import other class(sample.d.ts) in code.ts

Recently started to learn Figma Plugin where I could not figure not how to import a sample.d.ts file in code.ts

example: I had created a file called sample.d.ts which contains a function

function testing() { console.log('Hello') } export {}
Adding the following code in code.ts

///

import {sample} from ‘./sample’

sample.testing()

I see following error in the console
figma_app.min.js.br:5 Syntax error on line 13: Unexpected token
import { testing } from “./Sample”;