Single Site pointing to different domains

Ok the topic title may not be the correct way to say what the problem is.

I am helping someone with there wordpress site. Originally, the person who designed the site had three different sites on one domain like this:

abc.com/A
abc.com/B
abc.com/C

She has three different sites called

aaa.com,
bbb.com
and ccc.com.

When you typed aaa.com in the browser, the files for abc.com/A would show up and all the links would work accordingly with aaa.com as the main site.

In the general settings of the back office, the wordpress site name was abc.com/A but the site address was aaa.com. So under the domain names aaa, bbb and ccc, you didn’t know it was coming from the main domain abc.com.

She has recently moved those aaa, bbb and ccc domains to new hosting company and it is no longer working. How do I fix this without having to move the files from where they are now (abc.com/A, /B and /C) to what it was before so if I typed aaa.com in the browser all the links in that site would still show aaa.com but the actual files are in abc.com?

I have tried changing the site url again in general settings but I think that is not the solution maybe because it’s not working.

Sorry that is so confusing, hopefully someone can help me. I really want to fix this, it’s driving me nuts because the designer did it before but we can’t get a hold of him anymore.

Help please.. many thanks.