It’s been a while since I uploaded any Apps. As far as i recall...
When submitting an iOS App for publication, the developer must provide a support URL, wherein they are supposed to provide a means for customers to make contact.
I don’t know to what extent Apple’s review team actually validate the support URL, or confirm it really does contain contact info. In my case, you simply land on a fairly basic web page that includes a support@ email address.
I think the support URL is normally visible in the App store listing, as an ‘App Support’ link though - not sure- to see that link, you may have to be logged in, with the Apple Id you used to download.