Trust deposits are normally handled through LeanLaw, but if your firm utilizes bank syncing then you'll need to do some backend work. 

To start, we'll need to create the liability accounts for the Client/Matter (depending on your accounting level). Open the Matter's settings, and goto Access and Billing, then click on Setup Trust Accounting. Create the account, but do not include an Opening Balance unless otherwise specified.
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Verify that your deposit from the bank has been correctly recorded in QuickBooks, then open your Trust Account and View Register. Find the transaction you wish to move, and select it. In the dropdown indicated below, switch to the client's correct liability account, and save the edit. 

The trust balance for the Client/Matter should be correctly be displayed in LeanLaw's Trust Accounts. Verify that it is, and you're all set!