On the CDU RTE page, select SEND (LSK L3). On the page, you will then see a list of routes you have saved with the CDU (.RT (if there are any)), or select FLTSIM FPLS (LSK R6), which will list all the routes (.PLN) saved in Documents/Prepar3D v4 Files for P3Dv4, or Documents/Prepar3D v5 Files for P3Dv5