Basically, you probably can't - Windows searches a specific set of folders (including the current folder) when you tell it to run an application. These are located in the %path% Windows command variable, plus a couple of other folders:
https://stackoverflow.com/questions/27382626/where-is-start-searching-for-executables[
^]
And unless the application.EXE file is located in a folder that Windows searches then the only way to run it is to provide a path to it.
The best way to get round this would be to store the path to the EXE in a UserData folder (
Where Should I Store My Data?[
^] may help - the VB code is very similar) that your app sets on installation, and your other app can access to get the full path when you want to execute it.