How to import/enter opening balances of Expenses, Income and Cost of Sales into Quickbooks Online International

You may utilize an importer tool

https://transactionpro.grsm.io/qbo

Customer Accounts Receivable

First import your customer list to QuickBooks with the tool
Set up a default item in QuickBooks that uses an account called Opening Balance Equity. This is so the credit side of the entry does not post to sales but to a balance sheet account. You will provide this value in the tool mapping as a static value next to the QuickBooks field, Item.
You can then import all the open invoices as of the start date of the QuickBooks company file using the invoice import. If you wish you can bring in detailed line items or you can just have one line for each invoice with the total amount.

Customer Open Estimates and Open Sales Orders

Follow the same steps as outlined above under Customer Accounts Receivable.

Vendor Accounts Payable

First import your vendor list to QuickBooks with the tool
Set up an equity account in QuickBooks called Opening Balance Equity. This is so the debit side of the entry does not post to expenses but to a balance sheet account. You will provide this value in the tool mapping as a static value next to the QuickBooks field, Expense Account. If you use items on your vendor transactions follow the same steps as in the Accounts Receivable section above.
You can then import all the open bills as of the start date of the QuickBooks company file using the bill import. If you wish you can bring in detailed line items or you can just have one line for each invoice with the total amount.

Vendor Open Purchase Orders

Follow the same steps as outlined above under Vendor Accounts Payable.

Inventory Quantity on Hand

First import your item list to QuickBooks with the tool
Import your Quantity on Hand and Values using the import type, Inventory Adjustment.

Other Balance Sheet Accounts

When you first start the new QuickBooks company file you should first import the chart of accounts
Run a trial balance or balance sheet as of the last closed period and subtract out any balances already in the new QuickBooks company file to calculate the remaining balances to be imported.
Import these remaining balances as journal entries using the tool.

Good luck!