Currently, you can't use check box controls in Excel Online. If you're working in Excel Online and you open a workbook that has check boxes or other controls (objects), you won't be able to edit the workbook without removing these controls.
Important: If you see an "Edit in the browser?" or "Unsupported features" message and choose to edit the workbook in the browser anyway, all objects such as check boxes, combo boxes will be lost immediately. If this happens and you want these objects back, use Previous Versions to restore an earlier version.
If you have the Excel desktop application, you can use it to work with check box controls. Here's how:
Click Open in Excel and follow the steps in Add a check box.