Hey @John_Fishman,welcome to the forums.
A few things:
Virtual shifting via the Click and Cog will not work in SYSTM at this time (maybe ever).
HOWEVER , with that said, there is a way for you to do the 4DP but given your requirements to explain as if you were 5, I WILL fail. I’m gonna give it a shot anyway, cuz I like challenges 
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Before we get there though, you should know that most people with smart trainers use ERG mode for structured training. Unlike Zwift where you are riding in a simulated virtual world, where you shift gears to match the terrain you are riding, SYSTM does not provide a simulation of real world riding. SYSTM’s strength is their structured workouts (with some VERY engaging video to watch, and in some, music to listen to, while doing them). While Zwift does have a bunch of these it is NOT their strength. The vast majority of the SYSTM cycling workouts can be done in ERG mode where shifting gears is not done anyway. The trainer controls resistance and you just have to match the cadence target.
So, that aside (for now), if you want to take the 4DP test to make sure your workout targets are personalized, then there’s a workaround technique that you could try which has been used successfully on the Half Monty SYSTM ramp test: (Zwift Ride with SYSTM - #11 by Brian_Kraemer).
You need to understand that this technique will still not let you use virtual shifting, so you won’t be able to use the Click. You also won’t be actually shifting gears, virtual or otherwise, but you will experience a change in resistance based on your cadence that you will be able to adjust (sort of like changing gears but not really).
If I read you right, you are using SYSTM on a Windows PC? Yes?
If so, when you start a cycling workout from the Cycling Library (this will work on ANY cycling workout) you will see a gear icon at the top right of the screen. Tap that icon. From there, if you follow the directions for using Level Mode, you should be able to change levels where each progressive level provides greater resistance as your cadence increases. There is a keyboard shortcut that allows you to choose a Level on the fly using your number keys 0-9.
I’d suggest you try this on something like Open 30 from the cycling library and have a play with the different levels, experimenting with your cadence at each level. For example, try Level 0 and increase your cadence to see how much resistance is provided as you approach your max. If you find yourself spinning out because resistance is too low, then Level 0 won’t work for you when Sprinting (the first part of the 4DP test). Try the same thing again with Level 1 and keep going like this until you find a Level where you can reach what is close to a Max Sprint and the resistance feels about right.
Similarly, you can try different levels to experiment with different parts of the 4DP test. The second part of 4DP is a max 5 minute effort, the third part a max 20 minute effort, and the last part a max 1 minute effort.
This won’t be fun. It’ll feel like a real pain in the butt and a BIG hassle. But, once you’ve learned the Levels that will work best for each of the 4 types of effort of the 4DP test, you’ll have that knowledge for ETERNITY as well as for the next time you take the test (if you survive 
)
I could say more, but I’ve probably already lulled your 5 year old self to sleep.
Edit: also, fwiw, it might be worth editing your title to say SYSTM 4DP using a Zwift Cog and Click (sorta a flies with honey thing 
)