I don’t see any other WiiM app in the Google Play Store (although the Apple store does have a WiiM Pod app as well) but this forum is primarily if not exclusively for users of actual WiiM devices, not other Linkplay related devices such as your Fosi device, sorry. I’d go back to Fosi and ask them for a link to the correct app in the Google Play Store or for them to send you the apk of the app itself.
On a long shot, you could try the feedback section of the WiiM Home app and see if WiiM can point you in the direction of the correct app to use.