You will need to TEMPORARILY disable the "Install from Trusted Sources" in the settings and security section of the device prior to installing. Use the App, remove it, then re-check the "Install from Trusted Sources" in the settings.

These apps are provided without warranty from the official sources and are to be used if you are not able to install them from the play store due to issues such as google authentication, device issues or Play store issues.

Copy My Data APK (Official Play Version)

SMS Backup Plus (Official Play Version)