REN builds your schedule based on your availability and the training load you can handle. Whenever you move a workout, REN recalculates the rest of your week. Depending on which workout you move, this can lead to different outcomes.
If you move a hard workout (for example a HIT) from tomorrow to today, you'll do your HIT today and tomorrow will most likely show an easy endurance session. You've still set availability for tomorrow, so REN fills that day with a suitable, lighter workout. REN will never schedule two HIT or two CS sessions on back-to-back days, so you don't have to worry about doubling up on high-intensity work.
If you move an easy endurance workout from tomorrow to today, there's a good chance you'll get an easy endurance session both today and tomorrow. You've indicated you have time on both days, and REN calculates that you can handle this load two days in a row.
Don't want to train two days in a row? Adjust your availability for the day you want to rest. That way REN won't fill that day with a workout.
One more thing to keep in mind: a workout you move is pinned to its new day. Whatever else changes in your schedule after that, the moved workout stays put and won't be adjusted anymore.