Hi,
For that, please use the following code:
<a href="//your-site-url.tld/?wpdmdl=[PLACE-ID-HERE]" target="_blank" rel="noopener noreferrer"><i class="fas fa-file-mp3"></i></a>
Or use shortcode:
[wpdm_direct_link label='<i class="fas fa-file-mp3"></i>' target="_blank" id=ID]