The Enable suggested categorisation option may have been turned on, that's why it's categorising your bank transactions automatically. I'm here to guide you on how you can disable this feature, Admin327.

You can untick the Enable suggested categorisation box on your Bank transactions page to stop this. To do so, follow the step outlined below: 

1. Go to the Transactions menu on the left panel. 
2. Select Bank transactions.
3. From the For review tab, click the mini Gear icon.
4. From the Groups section, uncheck Enable suggested categorisation (Note: The screenshot below may be in US but it works more likely the same with the International version)
   
   

To give you more details on how to properly categorise your transactions, consider reading this article: Categorise Online Bank Transactions in QuickBooks Online.

After you have categorised them, you can now proceed with the next steps. Check out this reference on how to reconcile accounts in QuickBooks: Reconcile An Account in QuickBooks Online.

Keep in touch with me if you have other questions about categorising your bank transactions or any QuickBooks concerns by commenting below. I'm always right here to help you. Have a nice day!