How to keep the value of this when using async.apply?

I am using async.parallel to run 2 functions at once, which are run from a static function on a mongoose model. As you can see, I can this this to access the model and it's functions in this code (the model has a static function called verifyParent):

async.parallel([
      async.apply(content, {slug: slug}),
      async.apply(this.verifyParent, req.body.reply),
    ], (err, result) => {
          //results
});

But in the this.verifyParent function, if I try to use this, it's equal to my express app, and not the mongoose model. I beleive async.apply is doing this, and I can't figure out how to make it keep the this value it would normally have.

In verifyParent, I'm trying to query mongodb. When I run this.findOne(), it says it's not a function, and looking at this seems to indicate it's set the app, not to the model.

from How to keep the value of this when using async.apply?