Select the driver you want to drop for and click Driver Status.
The driver status window will appear. On the list of actions at the bottom select the "Drop" button.
The drop window will appear. On the top it will display how much money is estimated that the driver should have on hand, how much was assigned to the driver to begin with, and the recommended drop amount. On the right it will show the available buttons of tender that can be dropped. If there are credit card receipts the driver can drop those as well.
Select the tender type and then enter in the amount of money you would like to drop on the keypad, and then click "Drop".
The driver's financial summary will update to reflect the drop that was made.