Tips for improving a very flat affect?

As the title states, I have a very flat affect. I have been told that my natural way of speaking comes off cold and uninterested, even when talking to close friends and family. It really impairs my social life as people naturally assume I don’t like them and am not interested in our conversations. Virtually every friend I’ve ever had has told me that they thought I didn’t like them at first, and some have described me as “intimidating” (which is crazy to me, as I am extremely anxious in social situations and find everyone ELSE intimidating). I’m not usually one to put in a lot of effort to mask but I really want to learn how to stop talking like this so I stop giving people the wrong idea. Any suggestions?