Access 2 different SAP systems from SAP GUI

Hi,

I have a work computer using which I access various types of SAP systems (Dev, Test, Prod, CRM, BI, Solman etc.).

I have a need to access a 3rd party system (no relation to work) to learn something new.

When I try to map the 3rd party's server credentials (IP and Instance number) in the existing SAP GUI and access it, it does not work. It errors out claiming that the service is not recognized.

How do I go about accomplishing this if at all possible?

I am not a basis person and so not very familiar with various dll files that influence it.

Thanks,

UV