As a senior manager I worked closely with a VP of engineering on the engineering culture - one of the expected outcome was the improvement of our Glassdoor company rating. But my VP (and probably the leadership) wanted to go fast. So my VP was in touch with someone at Glassdoor and had a way to 'tweak' or remove unpleasant reviews. I don't know the details but if there is definitely a way for companies to do that despite Glassdoor claiming that reviews can't be removed.