When you try to update cells in Excel using Power Automate you could use the Update a row action.
Update a cell in Excel
In the past I’ve used MS Graph to do things with Excel spreadsheets with Flow.
When you use the update a row action to update cells in Excel, like with all other actions in this connector, you will need a table in your Excel spreadsheet. One additional requirement is needed for the update a row action.
You will need a key column with unique values.
In my example below I created a column key and populate this column with a number.
Now as I run my flow my row with the key equals 1 is updated.
Unique Key column
It is important that you have a Key column that is unique. When I updated the row with Key set to 1 while I had multiple rows having a key of 1 only the first row was updated.
Therefore make sure that you key column is unique and then this update a row action can be very useful.