Looks like this is duplicate of the thread How to connect to oracle database
Here is my answer:
Create TNS entry for the client database in the reports 6i environment. Then use the same in database connection. The entry needs to be created in tnsnames.ora file.
You need to put the client database TNS entry in your laptop, Where you have installed the Oracle Reports 6i,
You need to put entry like this in the above file,
(ADDRESS=(PROTOCOL=tcp)(HOST=hostname)(PORT=client database port no example:1521))
Then while connecting the Oracle Reports 6i
In the database option you need to mention the SID.