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. Before you enabled password protection, you had unlocked some cells in the workbook. Now that your boss is done with the workbook, you can lock these cells.
Follow these steps to lock cells in a worksheet:
Select the cells you want to lock.
On the Home tab, in the Alignment group, click the small arrow to open the Format Cells popup window.
On the Protection tab, select the Locked check box, and then click OK to close the popup.
Note: If you try these steps on a workbook or worksheet you haven't protected, you'll see the cells are already locked. This means that the cells are ready to be locked when you protect the workbook or worksheet.
Tip: It's a best practice to unlock any cells that you may want to change before you protect a worksheet or a workbook, but you can also unlock them after you apply protection. To remove protection, simply remove the password.
In addition to protecting workbooks and worksheets, you can also protect formulas.
Excel Online can’t lock cells or specific areas of a worksheet.
If you want to lock cells or protect specific areas, click Open in Excel and lock cells to protect them or lock or unlock specific areas of a protected worksheet.