1)Root your mobile(If already rooted leave it)
2)Install X-posed Installer,X Floating Windows and PA Halo))) By Omkar
3)Open X-posed installer,click on framework and then click on install/update and then go back and click on module and check xhalo floating window as in screenshot then reboot your device.
4)open floating app window and do settings as per your wish.
5)open PA halo by Omar click on PIN and choose applications you like to add & then click on START to enable floating app