[android] Android App Not Install. An existing package by the same name with a conflicting signature is already installed

If you don't want to bother with the keystore file, then just remove the package altogether for all users.

Connect your device with Mac/PC and run adb uninstall <package>

Worked for me.

Ref: https://android.stackexchange.com/questions/92025/how-to-completely-uninstall-an-app-on-android-lollipop