I tried the Domain Mapping plugin, but it did not work. So I installed WP again and created a new login, etc., though it wouldn’t let me use my websiteB.com domain b/c I already used it as a domain add-on. So I added a sub folder (websiteB.com/dir) & it worked. Then I had to go back into my 1st WP account & redirect the domain (website B) to the new link with the sub folder. Craziness! You’d think it would have been an easy solution. I wish I had never did the domain add-on to begin with & just installed & created a new log-on, etc, but that’s what my host & wp forums said to do. Two days of my life was spent figuring this out, but thankfully now I have two working websites!!
I could delete them both & start over, but I don’t want to risk the site not working again & going through the hassle a second time.