Is this mold from a water leak?
Doesn't look like mold to me but hard to be sure... If you're sure it's a small amount, and not the tip of the iceberg it's certainly DIY'able.  Diluted bleach works well as a treatment. Wear a respirator, remove as much as you can and then spray liberally with diluted bleach.  Ought to take care of it...

The way it's running out of the seam it looks more like mastic or something to me but I don't think a little bleach is going to hurt you either way for peace of mind.