Try running yes | someprogram. That's what yes is for, isn't it?

If you're so unlucky to be stuck on a Windows machine with no access to unix tools, you can try echo | someprogram instead. That has the disadvantage of outputting only a single line, so if your program is waiting for more, it may still get stuck: in that case redirect an input file with several newlines to it, such as <\path\to\yes.txt someprogram where you previously create the file yes.txt which contains lots of empty lines.

Remove the line from your code that is asking for the keypress. If you didn't write the code, and you don't know how to modify it, ask the author. Or as an alternative, post no more than ten lines of code showing how a keypress is being required so that we can advise accurately how to remove that constraint.