No Way To Delete apk from other phone . You have only way that give a app update if it’s on playstore . If it’s not in playstore than you have no way to give the update until you set the algorithm to do it. Or create new application
The only option would be to send your “friends” an update that contains an almost empty APK, but that requests WRITE permission, searches the /Download folder (or even the entire device via listing all APKs) for the old APK and (if there) removes it. After that there would be no way to reinstall the old version.
However, his friends presumably already know that he wants them to delete the app. In such a case would they want him to update it? Surely they are not silly enough to fall for the trick and believe that the update will make the app better.
As already mentioned he should delete the Firebase DB if it will solve the problem.
@Tvs_Group there is also another way if you can somehow manage to add a Gmail account(Gmail must also be on your device) in there device by asking them or making any kind of story then after that you can use find my device application to completely format their devices