Hi Stoop 57,
welcome to the Apple (user-to-user) Community!
Re: "Can I get the setup information for my custom domain resent to me?"
Am no expert in this area, yet your request deserves some response.
We don't know which computer or device you are using, or which OS is installed.
As you have posted your question in the iCloud Community:
one or more of the linked Apple Support "how to" articles below may be helpful to you:
Set up an existing domain with iCloud Mail - Apple Support
Use Custom Email Domain with iCloud Mail - Apple Support
Add an email domain you already own to iCloud Mail on iCloud.com - Apple Support
___________________________________________________________________________________
Else: You may want to browse the "Table of Contents" in the iCloud User Guide - Apple Support
All the best :-)