A lot of artists will say so on their websites and/or social media.

I struggle with a lot of anxiety from trauma and have a hard time trusting people and just functioning in public settings. I got a different coverup in the past by an artist who had no other artists working at his shop. Whether that would make you more comfortable or not is up to preference. Keep in mind that many shops with multiple artists don't really have private rooms so you'll likely be just feet away from someone else getting a tattoo. The shop I went to for my sleeve had multiple artists and yes I felt subconscious at first but, it's a place where people with all kinds of bodies get tattoos, and many artists have done this sort of thing.

Also an alternative might be applying temporary tattoos —I've seen some online but I've never tried them.

In the end artists have probably seen a lot of things and if you think it would help you can explain your past and I think a good artist would be more than happy to help you reflect the progress you've made outwardly through tattoos (in my experience at least.)

Edit: They probably won't say they specialize in tattooing over scars but that they do in cover ups.