With TC the temp is what you want to vape at and the wattage is how fast it gets to that temp.
I'd make sure the atty is vaping perfectly in power mode first. Basically you can chain vape it at your chosen power setting without any problem whatsoever. Then I would unscrew the atty, let it sit for 10 minutes to cool off to room temperature completely, cold base resistance is key to a properly working TC.
Set your Therion to the wire type in the atty, try 450F and 50W as a starting point and screw the atty on. The Therion should detect the New resistance and if it looks correct then say yes. If it's way off then try reattaching the atty again but I doubt this will be the case.
At this point you should be good to go, hit the fire button and see how the vape works. If the Therion goes to Temp Protect immediately, you have a problem with improper cold base resistance, wrong TCR value for the wire used (all SS can be different, even between batches from the same manufacturer) or you forgot to turn the juice flow on.

This will take loading a profile for said wire, resetting the cold resistance again etc.
Hopefully all is good and now it's just a matter of fine tuning you vape. I find that anyone who gets a great TC vape below 400F doesn't have a properly functioning TC. I usually run mine at 420F with the Jaquin UD SS316L wire profile V4 from the Evolv forum or around 450F with the stock Steam Engine 316L CSV profile. The wattage is up to you and will usually be the same or higher than what you use in wattage mode, but you can adjust either for taste.
Keep in mind that I only use TC these days on squonks and drippers as I'm lazy and have been bit too many times pulling on a dry RDA after setting it down then forgetting to rejuice the wicks.
When I did run TC on RTAs it was usually with Ti wire on Kayfuns, FeV, Ammit, Crius Plus etc. I do still run TC on the Russian Fusion RTA sitting on my Arctic Fox Pico.
The above should be a good starting point and it will take some tinkering to get it to what you like. TC is not for everyone, if you get it going and enjoy it that's all good, if not then that's all good too!