Sontex916 PDA software

Hi. I have Sontex Supercal 539 heat meter. Its service life is coming to an end but they don’t produce these anymore, so my next best replacement option is Supercal 739. The problem is that I am using a PDA with Sontex916 program to remotely read it and there is no option to select Supercal 739. Maybe I just have the old version, and in the new version it is added? But there is no way to get newer version of this software because Sontex doesn’t support it anymore.
What are my options?