Hello there, @accountant46. I'm here to ensure you'll be able to undo the reconciliation of your account in QuickBooks Online (QBO) seamlessly. 

To begin, could you tell me what QBO region you're using? Currently, the option to add an accountant in QBO global regions is unavailable. This may be the reason why you can't see the Accounting firms option. That said, you can only undo the reconciliation of your account manually. 

However, if you're using the QBO Plus US version and you're unable to see the Accounting firms tab. We can perform some troubleshooting steps to resolve this. 

Let's start by opening your QBO account in incognito mode. This is a private browser that does not store a cache and will give you a clean slate to prevent issues. Below are the shortcut keys that you can use:

• Google Chrome: Press CTRL + Shift + N.
• Safari: Press Command + Shift + N.
• Microsoft Edge: Press CTRL + Shift + N.
• Mozilla Firefox: Press CTRL + Shift + P.

Once signed in, go to the Manage users menu to check if you can now see the option. If this works, I recommend clearing the cache of your regular browser to eliminate the piled-up cache. This is a component of your browser that speeds up the loading process but sometimes gets corrupted resulting in odd behaviors when accessing the program. If the same thing happens, I suggest using another supported browser or device to open your account.

When the accountant is added, they can now start to manage your company file. 

I'd love to know how this goes. I'd appreciate any details you can provide. If you have any other concerns about undoing a reconciliation, feel free to post again here. I'm always around and ready to help. Have a good one and keep safe.