Follow below steps to convert QuickBooks Enterprise to QuickBooks Online:

Important: If any problem occurs during steps execution contact Customer Support for QuickBooks.

1. Open QuickBooks Enterprise Solutions so you see the screen listed below.

2. Press Ctrl+1 to open the Product Information window

a. Once opened, press Ctrl+b+q.

b. Click OK to close the Product information window.

3. The screen below should automatically come up. If you don't see this screen, attempt Step 2 one more time.

4. Enter your QuickBooks Online login info, agree to the Terms of Service, and click Submit.

5. Pick the online company you want to import your data into.

6. Note: You may only have the option to import list and balances if your company file is too large to import. If you don't see this screen, continue to the next step below.

For more information visit here- Convert QuickBooks Desktop to QuickBooks Online