Great question! I know how useful reports are for seeing the information you need in a set of books and I want to make sure you know your options when it comes to the reports you're running in your client accounts, as well as your own.
While there are many reports, such as the Balance Sheet Comparison report, that are available in all three QuickBooks Online packages, the report customization options can vary depending on whether the account is EasyStart, Essentials, or Plus (Note: QuickBooks Online Accountant accounts are based on a Plus package). I have a hunch that this is exactly what's going on here.
For instance, in a QuickBooks Online Essentials or Plus packages, you can see the customization options you're referring to under the Rows and Columns section. But this option isn't available in EasyStart, which has a more limited list of options. Check out the images below for a comparison of the customization options between Essentials/Plus and EasyStart on the report you're looking at.
Balance Sheet Comparison Report customization options in QuickBooks Online Essentials and Plus
Balance Sheet Comparison Report customization options in QuickBooks Online EasyStart
To make sure you have the built-in features you need, I recommend you and your client consider upgrading their QuickBooks Online account. I've got a couple articles here that can help with that whether your client is paying for their subscription themselves or whether you have them under your wholesale billing accounts.