Since this got me stumped for longer than I’m willing to admit, let me post the picture where the reset button of the Tempest is located (and where it is not).
As a suggestion for support, I would love to see a section at https://help.weatherflow.com/hc/en-us/articles/115005397428-Managing-Stations-Devices, with a photo for each device type (Tempest, Sky, Air) with the location of the reset button.
Right now, there are two descriptions on that page. Under “Re-pairing a device” it says “To reset a device and divorce it from the Hub, press and hold the clear button near the battery door”, which got me really confused (which battery door?). While under “If the device cannot be added successfully, perform a reset on the unit”, it does say “Press and hold the LED button on the base of the unit for 5 seconds then release after the LED flashes”. That makes sense to me, but perhaps not so much to a owner of a Sky or Air. 
PS: The forum was complaining that the title of this post “Reset a Tempest” “seems unclear, most of the words contain the same letters over and over?”. Hahaha, either you should turn off the “smart” features in this forum, or rename your product with more diverse vowels in the name 