Welcome to the site! You'd need to track the intervals separately. So if your workout had a total of 5 minutes at a certain speed and 5 minutes at another speed, I'd those in as 2 entries.
Hope that helps,
"You may have a fresh start any moment you choose, for this thing that we call "failure" is not the falling down but the staying down." Mary Pickford
"No matter how slow you go, you are still lapping everybody on the couch."