If you have protected areas of a spreadsheet against editing, you can unprotect them again.
Procedure
Open a spreadsheet.
Activate the Contents tab bar.
Select the area of the spreadsheet you want to unprotect.
You can select an entire row or column by clicking the row or column header. You can select rows or columns that are adjacent by holding down the Shift key.
Click Protect >
Unprotect.
The selected area of the spreadsheet can now be edited again.