Okay, a minor question, but I’ve got the sadness without it. Hoping someone can guide me. I used to have a custom notification on my Shopify app on my Android phone. Instead of the standard ding! notification when we got a sale, I had my own sound (Homer’s woo hoo!). After an update a while back (maybe 5 months?), it’s reverted to the standard Ding! and I can’t seem to find out how to fix it. I miss my Woo Hoo! 
Thanks so much for reaching out. However, yes, I’m going to have to ask for those screenshots you offered, as I can’t seem to follow it through the pages you describe. Just to be clear, I’m on an Android (in case it’s different on an iPhone or something)
Oops, looks like the one answer that was posted was deleted. Back to square one.
If you have Samsung, go to Folder and search “shopify”. You’ll find the cha-ching file. Should be in internal storage/notifications.