Just a reminder:
Once a device is listed as “placeholder“ in the IDE it is using the new architecture and you can no longer get to all of its details through the IDE. And if you try to edit it to make it use a Groovy DTH from the old architecture you can break the integration altogether. so don’t try to change its details there.
If you want to put it back to using a DTH, it will have to be a custom DTH with the same fingerprint. Because an edge driver now takes precedence over a stock groovy DTH.
So…
If you have a device using an edge Driver and you want it instead to use a Groovy DTH while those are still available, you have to first add a Custom Groovy DTH with that fingerprint to your account.
(If you were using a stock groovy DTH you will probably have to copy The code for that DTH, change the name of it, and save it to your account under the new name so it becomes a custom DTH.)
Now remove the device that is using the edge driver from your account. When you re-add it, it should pick up the custom groovy DTH instead of the stock edge driver. (And, yes, this means you will have to re-create any routine/automations that were using that device.)
But all of this is changing frequently during the transition, so it’s pretty much a fingers crossed process all the way through right now. 
But as of the date of this post, that’s supposed to work.
What definitely will not work is just trying to change the assignment through the IDE the way you used to do to change from one groovy DTH to another.
Remember that edge is still officially in beta until September 30, so anything you do now is subject to this kind of weirdness. 
I understand people wanting to start testing now, or getting ahead of the all in one day cutover, but you are reaching the “here be dragons“ territory on the map if you start manually using Edge drivers today rather than waiting for the system to do the transition for you at the official cutover date.


Your choice, but be aware that the IDE is part of the old architecture, and it has not been updated to work with the new stuff for edge drivers.