Random changing lockscreen

[Android Central Question]

Well ....I got oreo update for Samsung galaxy j5 prime.... and I like the feature that randomly changes lock screen wallpaper every time I unlock the phone ....these are total random pictures not from my gallery ....i don't know how do I started this feature in the first place ....now as I apply Samsung theme this feature vanished and I can't figure out how to re apply this fun feature .... I have gone through all setting option but still can't find any result .....please please please help ...