To protect cells in a spreadsheet
Excel for Office 365
Suppose that your boss wants you to protect an entire workbook, but also wants to be able to change a few cells after you enable protection on the workbook. By default a new worksheet has all the cells set to Lock, so when you use "Protect Sheet" in the Review tab all the cells are locked. So we need to "unlock" the cells we want your user to change before we protect the sheet.
Follow these steps to unlock cells in a worksheet:
Select the cells you want to unlock.
On the Home tab, in the Alignment group, click the small arrow to open the Format Cells popup window.
On the Protection tab, uncheck the Locked check box, and then click OK to close the popup.
On the Review tab in the ribbon, in the Protect group, select either Protect Sheet.
In the Protect sheet popup you can add a password to unprotect. This is normally not necessary unless you want to stop a user to changing this, and then click OK to close the popup.
Now you will find many of the options in the ribbon bar are unavailable and only the cells you have unlocked are able to be changed.
(Microsoft Office Support, 2018)
Microsoft Office Support (2018) Lock cells to protect them. Retrieved from https://support.office.com/en-us/article/lock-cells-to-protect-them-cb7835f6-9c37-4161-bb53-d1c410acaf21