How to implement Content-Disposition: attachment?

I am trying to make it so that mp3’s on my site are downloaded by left clicking instead of having to right click and save as, So in order to do that, I have to set the Content-Disposition: attachment. This is my first website so I am new to how to actually do this, but do I do this in my html markup or do I set this somehow with my hosting site?

Content-Disposition:attachment not triggering download dialog

I’ve encountered some unexpected behavior when trying to create a file download functionality on my NodeJS server.
I have a REST (express) API that calls for some export data function, which creates a CSV file on the server and uses'path/to/file') to trigger the download.
Response headers include