There are 2 types of overrides:

•  Flat – The manager gets a flat commission percentage based on all sales of selected reps.
• Rule Based - The manager’s commission is built into an individual commission system that will base the manager's a commission on the rules set within the commission plan and on the sales of the reps within the same commission system.

To configure either type of Manager Override Commission, begin in Tools > System Configuration > User Setup. Search the manager’s name, select from the tree below, and click Edit.

Next, go to the People Manager tab and expand the manager’s Region & Office.  Find the name of the sales rep the manager will be getting commissions from, and expand the + sign. Check “Managed” and Save.

To configure a Flat Commission:

In User Setup, enter the name of the sales rep you just assigned to a manager, select & click Edit. Go to the Commissions Tab and in the Default Rate section, look for Manager Override (Manager Name). To the right is a field labeled Flat %. Enter the commission percentage that will be allocated to the sales manager:

Option 2. 

A Commission Plan can be set up and marked “For Manager Override”

Then under User Set Up select the commission plan from the  “Calculate from Plan” dropdown.

Manger override means that a manager gets a commission from the sales reps he manages.