Plsql connection of database names on different IPs when connecting to Oracle

In the work sometimes through the Plsql connection database name is the same, but on different IP hosts, so, how to differentiate the connection by plsql? Such as:

See the picture, you will find that there are three different hosts are called ORCLBJ Library, and the database in the Plsql display is not the same, then we want to connect to a specific library how to distinguish it?
The specific solutions are as follows:
If you installed Oracle with a default installation, you can find Tnsnames.ora. Its directory is as follows: C:\oracle\product\10.2.0\client_1\NETWORK\ADMIN.
Such as:

When you open the Tnsnames.ora file, you can see the aliases for the specific database.

Plsql connection of database names on different IPs when connecting to Oracle