There are 2 ways to transfer items between warehouses.
With a transfer order, you end up with a shipment from warehouse A that needs to be packed and shipped using the apps and a PO in warehouse B for those same products that need to be received.
To create a transfer order go to https://app.shiphero.com/dashboard/orders/add and for Order Type use Transfer Order
With an instant transfer, the items instantly move from one warehouse to the next. To do so go to https://app.shiphero.com/dashboard/warehouses/transfers and hit Create Warehouse TO Warehouse Transfer