How do I get time capsule to work when upgrading to new I-Mac?

When you first boot the new Mac, you'll be prompted to set it up from a Time Machine backup of another Mac, among other options. Do that. It will inherit the backup history of the old machine. Connect to the Time Capsule with Ethernet, if possible, as it's much faster than Wi-Fi.

I'm not sure I really understand your question, but maybe this will help you:

"Reconnecting" to your backups