ONeed help with quintile in Excel or Power Query

Hi team, 

Hope you're doing great. So, I have a question. I'm trying to automate a similar dataset, where I try to categorize the skillset based on their scores while making sure that I only calculate for the rows with the same skill name.

Let's just say, I have a dataset with 3 columns, 'Skill', 'Name' & 'Score'. here, what I'm trying to do is, create a new column that categorizes their quintile and assigns A, B, C, or D only based on what their skill is showing. 

Let's take the 'Draw' skill, we've 5 rows for that, so I want scores categorized into a, b, c, and d categories just for that. And then the next skill 'Paint'and so on. 

I'm trying to automate this, so Power Query would also be good, let me know what would be a good way to do so.