Hi, @jwhtng2112.
Welcome to the Roku Community!
Thanks for reaching us about the mounting plate on your device. We're here to help.
Do you have the letters D and E? Since these are the flat mounting plates that are included in the box.


Furthermore, you may visit this support article on how to set up your Roku Wire-free Video Doorbell and Chime SE
If you don't have one, please let us know.
Thanks,
The Roku Community Team
Reynan L.
Roku Community Moderator