if you mean the sounds themselves, they were created by Sam Tudor, who made all of the music and sfx for HIKEBACK!
if you're asking how i made them play while dialogue showed, i'd recommend going through the Ren'Py cookbook to try out some of the programming techniques there to help answer your question. i used this page as reference, although it's now out of date, so you'd have to adjust it to modern ren'py haha