So it is actually pretty easy to change or delete a rating once it has been submitted. Because on the one hand, opinions sometimes simply change after you have had very positive experiences with the company later, or the other way around, everything is much worse and you want to express your displeasure.
However, always make sure to remain factual in your reviews. Please do not start with personal mention of names, or worse, utter insults.
So if you write for example:
Mr / Ms XYZ is the greatest id … t ever walking around. How can such a sh…t company survive ??? !!!,
then this is not only irrelevant, but can also cause legal problems due to your insults. In case of doubt, such reviews are rightly not published by Google. Because the possibility of submitting reviews does not serve to get rid of your frustration, but rather to help the whole community with your experience in the decision-making process.