Do you mean to do a replenishment that is not automatic? So when a product goes below a certain quantity in a warehouse users (who probably have access to only those warehouse operations) can request for more to be transferred? 

If that is the case then in addition to creating a new operation as others have suggested you need to create a new route that pulls from your WHA to WHB and set it so it can be selected on products. Then when products are needed in a WHB it can be ordered from the replenishment page by manually putting in the quantity and selecting your new route. A new picking with the appropriate operation will automatically be created and will be in ready state. 

Let me know if it wasn't clear

Hi,

Please see here => https://www.youtube.com/watch?v=F4nppNqDg2A

This will do the same, transfer products between warehouses and with route.

You can go to the menu: Inventory / Operations / Transfers

Create a new one, and fill the required fields. Choose "Warehouse (A or B) - Internal Transfer" as "Operation Type". Be sure to give a proper value to the other fields. 

Hello

Were you able to create this process without a customisation?

We are running a similar operation, and want to create a demand based internal transfer system between our warehouses.

Vikrant