one option is you can download the S secure app from the galaxy store and proceed. another one is you can download activity launcher from playstore and by opening you'll find an installed app named App lock in your phone which is hidden. click on that and launch the activities you'll get an option to lock your apps after which you can uninstall the launcher app after your work getting done. But remember one thing this app lock is not much secure why I'm saying note that the app only locks when you off you screen. It means that after unlocking a app until you turned the screen off your apps will not get locked
