@Narculis
Yes, you cannot actually rename a column in SharePoint. It might look like you did (as there is an option to rename), but behind the scenes, it will always have the original name. So, when you import from Excel, it will create all the columns as field_x. In many cases it will then try to "rename" them, or you end up doing it, but the column will always be field_x.
To determine a column's real name, you can click on the column in the List Settings of your list and then in the address bar of your browser, look at the end of the URL - it will show the real name.
That OnSelect action of your PieChart is not a "default" action. That had to be added.
So, as for your chart...
If you want to show the counts of the assets by employee types, then you need to group on the employee types.
So, you Items formula on the PieChart needs to become:
AddColumns(
GroupBy('Master Asset List',
"EmployeeTypeColumnName",
"_assets"
),
"_counts", CountRows(_assets)
)
Your Labels will then be the employee type column name and the series would be "_counts".