How to add New MIME Type (.Arena)?

[Zion1]

Hello everyone, I am trying to add a new mime type which is .ARENA, I tried following a previous thread on this but it's not working for me. When I try to download the .ARENA extension it just leads me to some words instead of downloading, I need it to download instead. I can't find much on this extension as a mime type, but it is for a game I play.