You will see the new device handler (formerly called a smart device type) in the IDE, which is a developer tool. You view it through a web browser, not through the phone app.
You should have created it through the IDE as well, so you go through the same process to sign in.
Some custom device types will automatically be assigned to a new device when it is paired. These are usually zigbee devices.
For the others, you sign in to the IDE and follow the instructions in DH5 and DH6 above.