Start by looking in IDE. Any Device that shows Placeholder is using an Edge Driver or is a device connected through a Linked Service that is now on the new architecture. You do not need to do anything with those.
Next you need to install Edge Drivers on your hub. To do this, you will need to subscribe to the Channels from ST or Community Developers. Once subscribed, You can select the Edge Drivers you wish to enroll. To find the Channels, search through the forum to find all the Community Developed Edge Drivers and they should include a link you click on.
After you install the Edge Drivers, now comes the fun part. You will need to remove the Devices from ST. If you are using a custom Device Handler for it in IDE, you will need delete the Device Handler there OR comment out the fingerprint of the Device in the DTH before you can add the devices back. The reason for commenting out the fingerprint is where you might have multiple devices where you don’t want to convert them all at the same time. Either way, custom Device Handlers need to be removed or fingerprints commented out before you can add Devices back so they get the Edge Driver.
Add the Devices back by using the Scan option. After they are found, they will display as Placeholder device type in IDE and you can no longer manage them there. Instead, open the device in the ST app, tap on More Options (the 3 dots in the upper right of the screen, and you will see “Driver” listed in that pull down menu. This is where you can switch to other Edge Drivers if needed.
If you are using any custom Smartapps that connect Devices would need to have their devices switched to Edge and those smartapps removed.
https://thingsthataresmart.wiki/index.php?title=Table_of_Edge_Drivers