This is quite easy. Just go to Cognos Express Manager (https://servername:19300/cognos_express/manager/), click on Data, Select the Data Source Type as TM1, then enter the name you want to call it in BI, the servername as the Administration Host, the TM1 server name (“CXMD”), the TM1 cube name you want to add to BI and finally the namespace (“CognosExpress”).