New FTP user on single domain

I’m having an issue and just want to see if there is anything I can do to fix it. I have three domains on my plan with DH. Obviously, I can access all of them via FTP. I am taking on a partner for one of my domains and would like them to be able to access files on that domain via FTP but not access the other domains. I figured I could set up a new user that we could both access and set it up so the domain is under that user. But I have been running this site for awhile already and have files uploaded. I was wondering if there was a way to have the new user access that domain and the files that already exist without having access to my other domains. This is the only issue I’ve ever had here and it’s frustrating because I never had a problem setting up FTP users before.

Wiki article here

The only way to do this is to create a new FTP user that you both share for the domain in question, move the files from the current user directory to the new user’s directory and you both use the new FTP login and directory, keeping the other domains seperate in the prior user record.

It’s one of the slightly annoying shortcomings of the FTP service here, but it’s not insurmountable.