Domain mapping stoped working , tried everything to restore functionality with no success

I’m requesting assistance with mapped domains. Would appreciate if someone could log in and show me where I went wrong.
And a step by step of how to add a new on would be helfull.
Last October I decided to try mapped domain, on my new host.
After a few snags, I did succeed. Later I add a second map domain.
After testing those two mapped domains, with all the plug-ins that I intend to use. Everything looked good.
Two weeks ago I decided to try to add to two live customer sites.
This is turning out to be a nightmare.
The first stage of setting up the new sites works flawlessly.
Sitename.root-domain.
I noticed that one of the working domains was parked. I changed it and broke it. And can no longer map that domain.

I have screen shots which I will try to attach.
Thanks Ron