I pulled a 2477D INSTEON Dimmer switch from my box of unused devices to add it to my condo and the address label is unreadable. How do I add this to my EISY if I do not know the device's address?

In admin console, click on:

Link Management

Start Linking

At this point you press and hold the set button on the switch and it will pop up on the screen to be added.

@Kentinada Further, once you have it in the AC, you can see its address adn then write it on the switch for future reference.

I put my Insteon devices addresses in a database besides marking it in the module. Mine where worn off on the remotes. Also real old ones had paper stickers that liked to fall off.

Creating a Topology report will give you all device addresses and lots of useful additional info

TOOLS | GENERATE TOPOLOGY