Decompiling a 16-bit dos application

I have a very old application that I bought about 15 years ago, it consists of 5 .exe files used to store patient profiles and information. The problem is that this application has been programmed to work on a specific computer.
And since I have little knowledge about hacking, I tried to parse it using win32dasm, but there was no information about string links, I tried Hiew to replace JE with JNE, and after many attempts one of the executable files worked, but I could not fix other files .
Is there a way to find the exact jump and fix it?
thank;)