LeanLaw can import any client and sub-clients from Quickbooks Online.
A LeanLaw client is a QuickBooks client.
A LeanLaw matter is what QuickBooks calls a sub-client.
Open up your Settings, included in the gear icon at the top right.
Open the QuickBooks Integration tab on the left, then scroll to the bottom.
Click the Import Clients From QuickBooks button, and follow the prompt.
Below is a screen shot of LeanLaw's importing tool. You can either import all clients/sub-clients or select a subset. Once selected, you will have the opportunity to either create new LeanLaw clients and matters or associate with existing LeanLaw clients and matter.