Want to set up the new tnsnames.ora path for a PB application

I have 2 Powerbuilder applications in my machine and both using oracle 11g client. Now I have installed oracle 12c client so that the 2nd application can work with oracle 12c and the first one to continue working with oracle 11g. Before the oracle 12c installation there was only one tnsnames.ora file in the Oralce 11g folder. Now i have placed the new tnsnames.ora file in my 12c oracle installation folder but my 2nd powerbuilder applciation still refers the old one. Kindly help me on how to make my 2nd applciation to point to the 12c tnsmanes.ora file. I'm unable to find where the tnsnames.ora file path is set in my pb application.