Connect on the same server alias but with a different user schema

Hello all,

When I use Power BI, I connect a report to an Oracle user schema to retrieve a view. The user schema (DB1) is located on a particular server S1. On this server there are several user schema. Now, I want to connect to another user schema (with different DB credentials) called DB2. However, when I type the server TNSName on the prompt to connect to Oracle DB, I'm automatically connected to DB1, so there is no way I can retrieve data from DB2. Grants from DB2 to DB1 is not an option. 

Can anyone know how to connect to the same Oracle server but with different user schema ? (Btw, connecting to another server is ok, but the same problem exists if I try to switch user in the second server...)

Thanks !