How to apply HDRI(env)?

Use RGBEloader to load the .hdr file, and in callback function use PMREMGenerator to generate the map from this HDR file. Then set the envMap parameter for your physical material:

let generator = new THREE.PMREMGenerator(renderer);

new RGBELoader().load('textures/gothic_manor_02_2k.hdr', (hdrmap) => {
    // ...
    let envmap = generator.fromEquirectangular(hdrmap);
    const ballMaterial = {
        // ...
        envMap: envmap.texture
    };
});