You may transfer all accounts owned by a specific reseller with the following steps.
1. Log in to WHM on the destination server as the root user
2. Navigate to: Home »Transfers »Transfer Tool
3. Enter the connection details for the source server
4. Click the "Scan Remote Server" button
5. Above the table that shows all of the accounts, click on the Packages tab
6. Select all of the packages for the reseller. Those packages will be prepended with the reseller's username.
7. Click on the Accounts tab to go back to the list of accounts
5. In the table of accounts, click on the "Reseller" header to sort the list by reseller name
6. If necessary, increase the page size with the dropdown at the upper right corner of the Accounts table
7. Place a checkmark next to each account that is owned by the reseller
8. Locate the reseller account as well and select it for transfer
9. When ready, click the blue "Copy" button at the bottom left to start the transfer