If the background is constant and indistinct, and you have a clean plate from later in the shoot, you could layer your clean plate on top of the hair and use the pen tool to draw a feathered mask around the part you need to cover. If the hair is small/thin enough and your background isn’t too detailed, you might be able to get away with that. Hard to say without seeing the shot.
If your backgrounds simply won’t match, there’s always the tedious approach of using the clone stamp tool in After Effects, or opening your movie in Photoshop and stepping through the frames, using whichever retouch tools you’re most comfortable with. I’d suggest making your camera assistant do it. Good learning experience.