Each Travel Agent can have it's own commission rate. When a booking is associated to a Travel Agent and completed and checked out, the commission rate is calculated in the Travel Agent commission report. Set this by entering the Setup Area, choose relationshiops, then MyAgents. Note that you can edit the "Commission Rate" specific to each Travel Agent that you have entered. You cannot edit the values to OTA channels that are master channels in BookingCenter. https://mypms.bookingcenter.com/site_agents.phtml
It's important to know that the commission amount for a booking is only applied to COMPLETED bookings. This means that a booking currently ACTIVE will not appear on the Travel Agent Commission Report. Nor will any CONFIRMED, UNCONFIRMED, or CANCELLED bookings.
Also, the commission value takes only the total amount of ROOM RENT (the RENT item that is applied automatically by Night Audit) and does not take into account any additional charges, such as food or beverage.
When assigning the commission value to the Agent, keep in mind that if you change the commission amount for the Agent, and then run the Travel Agent Commission Report, you will see that the new commission amount is displayed. So, take care when changing commission amounts and make sure past bills are paid up at the old commission amount before changing the commission number for an Agent.