How can I post opening balances for GL accounts as I have loaded a new chart of accounts?

Welcome to the Community, @anthony-healey. I have the steps you need to post opening balances for your GL accounts in QuickBooks Online (QBO). 

You're on the right track in importing your chart of accounts from another software into QuickBooks. Let's go to the Chart of Accounts page so you can enter opening balances for them. I'll guide you how. 

1. Go to Accounting from the left menu.
2. Select Chart of Accounts.
3. Locate your bank or credit card account.
4. Select the Account history drop-down from the Action column. 
5. Choose Edit.
6. Enter the opening amount in the Balance field. 
7. Type in the starting date in the as of box. 
8. Click Save and Close.
9. Repeat the process for your other GL accounts. 

The screenshot below shows you the sixth to eight steps. For detailed instructions, see Step 5 through this article: Move Your Chart Of Accounts To QBO. 

Once done, you can connect your bank or credit card accounts to the program. This way, the system will automatically download your transactions. Then, all you have to do is review and approve the work.

Aside from the chart of accounts, you can also import your customers, suppliers, inventory, invoices, and bills to QBO. For more details, visit this website: Conversion Process Overview. It contains answers to the common questions about importing data to QBO. 

Please know that I'm here anytime you have other concerns. Wishing you and your business continued success while using QuickBooks, @anthony-healey.