Welcome back, Lukes_mum,
I know when it comes to reconciling that the numbers require the utmost accuracy. Entering a missed opening balance is the perfect way to ensure that you're good to move forward with the task, and I'd be happy to guide you on how to resolve this situation in your new QuickBooks Desktop company file.
I'll start with the option you're seeing on the Edit Account window to Change Opening Balance. When you click that button, it simply takes you to the entry in the account register where you can make the changes as needed. When you've already entered an opening balance in, changing it would result in warnings about how it will affect reconciled transactions and the process as a whole.
What you've got with entering the transaction directly into the account register is the right idea, but in this case, the steps are going to be a bit different to register the opening balance. To start, delete the transaction you created and then follow the Recreate the opening balance section of the following article: Fix beginning balance issues in QuickBooks Desktop
Once you've done that, you should be good to go with reconciling the account. Give it a shot and let me know how it goes. I'm here to help!
