Below are simple steps to create RMA in Oracle Apps
Navigation > Receiving > Receipt >Go to Customer Tab > Enter RMA #
Press Find Button
In the receipt Form , you can see all the open lines for RMA.Check the line for which you want to create RMA , Update the quantity if required ,
Enter the Location and other details based on your setup Press Save button.
On Save , system will uptomatically submit the "Receiving Transaction Processor" concurrent Program.This CP on completation update the inventory , progress workflow from "Wait for receiving activity" and push the credit memo data to AR Interface tables as well as update the fulfill quantity on the order lines .