You don't want to slow down every word. Try these tips instead. :)

1. Self awareness is key. Record your presentation and then listen to it.

2. Deeply breath with you belly to calm yourself.

3. Pause 3 beats after every sentence.

4. Try reading poetry.

5. Listen more even if it is to yourself.

6. Find a buddy with whom to practice.

I hope this helps. I do this consciously when I teach so that my students understand and process what I am saying. It's important for your audience to comprehend you. Good luck! :)

A simple method is to record yourself - video or just sound, and then replay it to yourself.  Do you think you sound fast, normal or slow?

In school, kids who take part in plays are always being told to slow down, most people just want to say something as fast as possible, sometimes down to nerves, sometimes down to their brain working that fast, and there are many more reasons.