You Cannot change data inside a pivot table
When you click Drill Down in the PivotTable
As far as I know, you have to change the data in the cells of a regular table that is bound to Piot table then refresh the Pivot table itself to display these changes:
If I misunderstand please clarify.
Pivot Table is the tool that allows you to reorganize the data of your spreadsheet. The overall functionality may differ from regular tables.
Please take a look at the complete guide about Pivot Tables from our official Help Center: