Just got a power meter and watched a vid on how to send your workouts to do outdoors. The video wants me to make a new data screen with 4 boxes: elapsed time, 3s power, lap power, and time to go. The Epix does not have the time to go field.
What is the workaround for this, if there is one?
Workout Fields - Step Duration might give you something similar that must be compared to lap time.
Congrats on the new power meter! I think you’ll find it really helps you dial in your bike training. 
And jeez, I think you’re right that the Garmin epix doesn’t have a “time to go” option. I was just checking out all of the available data fields that Garmin lists, and it doesn’t look like it exists.
I think “Step Time” under “Workout Fields,” as @KevinKlaes said, might be your closest option. “Interval Time” under “Timer Fields” could be another one to check out.
While “time to go” isn’t a necessity, it certainly is useful information to have. It might be worth writing down the duration of your intervals on a piece of paper/tape and sticking it to your stem so you can at least know how long your efforts are supposed to last, and then you can use the timer on your watch to keep track. That’s what I used to do before I got one of the more recent generations of cycling/sport computers – it’s pretty “old skool,” but it gets the job done!
It could also be worth getting in touch with Garmin Support about this issue – they might have some useful suggestions as well.