You can use the following guide as well:
To add a password to an Excel file in Windows you need to open the File menu
Next. Select Info, followed by Protect Workbook and then Encrypt with Password
You’ll be asked to enter the password twice
After clicking OK and Save the document will be saved with the selected password.
Make sure you remember the password, as it can’t be recovered.
In order to open the document, the password will need to be reentered.
