How can I match imported deposits to existing customer payments? Had to disconnect our bank due to an update and reimport our transaction hisotry.

Welcome to QuickBooks Community, southernlawnapc.

I'll be more than happy to guide you in matching the existing customer payment to the imported transaction. This process will link them together so you don't get duplicates. When you're ready, here's how:

1. Go to the Banking or Transactions menu.
2. Select the Banking tab, then choose the tile for the account you want to review.
3. Head to the For review tab to start your review.
4. Find the imported transaction, then select it to expand the view.
5. Click Find match, then review the matching records found in QuickBooks. 
6. Select the customer payment, then make sure this is the correct match.
7. Click Save to match the transactions.

I'm also adding this article to use bank rules to automatically categorize transactions from your bank: Set up bank rules in QuickBooks Online.

If you need more help in managing your bank accounts and transactions, don't hesitate to visit the Community again. Take care and have a great rest of the day!