Hello there, @Slfike.

Since the accounts are already connected in QuickBooks Online you'll have to upload the transactions.

Here's how: 

1.  Go to the Banking menu.
2. Select the Banking tab.
3. Click the blue tile for the account you want to upload the transactions into.
4. Select the Update ▼ and then File upload.
5. Follow the onscreen instructions.

After that match and categorize the transactions, by going to the banking menu. 

For future reference on how to resolve issues in uploading transactions and steps to do if you're unable to download transactions in QBO, please check these articles: 

• Fix bank upload errors
• What to do if bank transactions won’t download

If there's anything else that I can help you with, please let me know in the comment section. I'll be here to lend a hand. Take care always.