Hi there, SMG.

I can help you link downloaded check with your existing transaction in QuickBooks.

You can manually match your downloaded transactions and make sure to select the Match to Existing Transaction and choose the transaction you want to match with the deposit.

Here's how:

1. Go to Banking.
2. Choose Bank Feeds.
3. Click Bank Feeds Center.
4. Choose a bank account.
5. Click the Transaction List button.
6. From the Action drop down arrow, choose Match to Existing Transaction.
7. Choose the transaction you'll want to match then click Confirm Match.
8. Click Yes.

I've attached some screenshots below so you can have a better view.

To learn more about matching transactions in QuickBooks, you can check out this article: Add and match Bank Feed transactions.

That's it. Should you need more help with matching downloaded transactions in QuickBooks, just let me know. I'm always here to help you out.